PLATE I

Mary Wellman, del.

PLATE I.

SPHINX-MOTHS.

1 = Pholus pandoras.

2 = Smerinthus geminatus.

3 = Ampelophaga versicolor. 4=Marumba modesta.

5 = Hemaris thysbe.

6= Thy reus abbotti.

.yinobnsq eMorN - .auiJsniriT*^ 2

.lolooia^y ‘sMiqokx ■ ••• r,

•

AMERICAN

INSECTS

BY

VERNON lY KELLOGG

Professor of Entomology and Lecturer on Bionomics in Leland Stanford Jr. University

WITH MANY ORIGINAL ILLUSTRATIONS BY

MARY WELLMAN

NEW YORK

HENRY HOLT AND COMPANY

1905

Copyright, 1905,

BY

HENRY HOLT AND COMPANY

ROBERT DRUMMOND, PRINTER, NEW YORK

TO

JOHN HENRY COMSTOCK

PREFATORY NOTE

If man were not the dominant animal in the world, this would be the Age of Insects. Outnumbering in kinds the members of all other groups of animals combined, and showing a wealth of individuals and a degree of prolificness excelled only by the fishes among larger animals, and among smaller animals by the Protozoa, the insects have an indisputable claim on the attention of students of natural history by sheer force of numbers. But their claim to our interest rests on securer ground. Their immediate and important relation to man as enemies of his crops, and, as we have come to know only to-day, as it were, as- a grim menace to his own health and life — this capacity of insects to destroy annually hundreds of millions of dollars’ worth of grains and fruits and vegetables, and to be solely responsible for the dissemination of some of the most serious diseases that make man to suffer and die, forces our attention whether we will or not. Finally, the amazing variety and specialization of habit and appearance, the extraor¬ dinary adaptations and “ shifts for a living” which insects show, make a claim on the attention of all who harbor the smallest trace of that “ scientific curiosity” which leads men to observe and ponder the ways and seeming of Nature. Some of the most attractive and important problems which modern biological study is attacking, such as the significance of color and pattern, the reality of mechanism and automatism in the action and behavior of animals as contrasted with intelligent and discriminating performances, the statistical and experimental study of variation and heredity, and other sub¬ jects of present-day biological investigation, are finding their most available material and data among the insects.

This book is written in the endeavor to foster an interest in insect biology on the part of students of natural history, of nature observers, and of general readers; it provides in a single volume a general systematic account of all the principal groups of insects as they occur in America, together with special accounts of the structure, physiology, development and metamorphoses, and of certain particularly interesting and important ecological -relations of insects with the world around them. Systematic entomology, economic entomology, and what may be called the bionomics of insects are the special subjects of the matter and illustration of the book. An effort has been made to put the matter at the easy command of the average intelligent reader ; but it has been felt that a little demand on his attention will accomplish the result more satisfactorily than could be done with that utter freedom from effort

VI

Prefatory Note

with which some Nature-books try to disseminate knowledge. The few technical terms used are all explained in the text in connection with their first use, and besides are inserted in the Index with a specific reference, in black-faced type, to the explanation. So that the tyro reading casually in the book and meeting any of these terms apart from their explanation has only to refer to the Index for assistance. Readers more interested in accounts of the habits and kinds of insects than in their structure and physiology will be inclined to skip the first three chapters, and may do so and still find the rest of the book “easy reading” and, it is hoped, not devoid of entertain¬ ment and advantage. But the reader is earnestly advised not to spare the little attention especially needed for understanding these first chapters, and thus to ensure for his later reading some of that quality which is among the most valued possessions of the best minds.

In preparing such a book as this an author is under a host of obligations to previous writers and students which must perforce go unacknowledged. Some formal recognition, however, for aid and courtesies directly tendered by J. H. Comstock of Cornell University, whose entomological text-books have been for years the chief sources of knowledge of the insects of this country, I am able and glad to make. To my artist, Miss Mary Wellman, for her constant interest in a work that must often have been laborious and wearying, and for her persistently faithful endeavor toward accuracy, I extend sincere thanks. To Mrs. David Starr Jordan, who read all of the manuscript as a “general reader” critic, and to President Jordan for numerous sugges¬ tions I am particularly indebted. For special courtesies in the matter of illustrations (permission to have electrotypes made from original blocks) I am obliged to Prof. F. L. Washburn, State Entomologist of Minnesota (for nearly one hundred and fifty figures), Prof. M. V. Slingerland of Cornell University, Dr. E. P. Felt, State Entomologist of New York, Mr. Wm. Beutenmiiller, editor of the Journal of the New York Entomological Society, and Dr. Henry Skinner, editor of the Entomological Newrs.

Vernon L. Kellogg.

Stanford University, California,

June i, 1904.

CONTENTS

CHAP. PAGE

I. The Structure and Special Physiology of Insects . . i

II. Development and Metamorphosis of Insects . . . 35

III. Classification of Insects . 52

IV. The Simplest Insects (Order Aptera) . . . . . 58

V. May-flies (Order Ephemerida) and Stone-flies (Order Plecoptera). 65

VI. Dragon-flies and Damsel-flies (Order Odonata) . 75

VII. The Termites or White Ants (Order Isoptera) . 99

VIII. Book-lice and Bark-lice (Order Corrodentia), and Biting Bird-lice

(Order Mallophaga) . 111

IX. The Cockroaches, Crickets, Locusts, Grasshoppers, and Katydids

(Order Orthoptera) . 123

X. The True Bugs, Cicadas, Aphids, Scale-insects, etc. (Order Hemip-

tera), and the Thrips (Order Thysanoptera) . . 163

XI. The Nerve-winged Insects (Order Neuroptera), Scorpion-flies

(Order Mecoptera), and Caddis-flies (Order Trichoptera) . 223

XII. The Beetles (Order Coleoptera) . 246

XIII. The Two-winged Flies (Order Diptera) . 30 1

XIV. The Moths and Butterflies (Order Lepidoptera) . 358

XV. The Ichneumons, Gall-flies, Wasps, Bees, and Ants (Order Hymen-

optera) . 459

XVI. Insects and Flowers . 562

XVII. Color and Pattern and their Uses . . . 583

XVIII. Insects and Disease . 615

Appendix: Collecting and Rearing Insects . 635

Index . 649

vii

AMERICAN INSECTS

CHAPTER I

THE STRUCTURE AND SPECIAL PHYSIOLOGY OF INSECTS

ERHAPS no more uninteresting matter, for the general reader or entomological amateur, can be written about insects than a descrip¬ tive catalogue of the parts and pieces of the insect body. And such matter is practically useless because it doesn’t stick in the reader’s mind. If it is worth while knowing the intimate make-up of a house-fly’s animated little body, it is worth getting this knowledge in the only way that will make it real, that is, by patient and eye-straining work with dissecting-needles and micro¬ scope. This book, anyway, is to try to convey some information about the kinds and ways of insects, and to stimulate interest in insect life, rather than to be a treatise on insect organs and their particular functions. Life is, to be sure, only the sum of the organic functions, but this sum or com¬ bination has an interest disproportionate to that of any of its component parts, and has an aspect and character which cannot be foretold in any com¬ pleteness from ever so careful a disjoined study of the particular functions. And so with the body, the sum of the organs: it is the manner and seeming of the body as a whole, its symmetry and exquisite adaptation to the special habit of life, the fine delicacy of its colors and pattern, or, at the other extreme, their amazing contrasts and bizarrerie, on which depend our first interest in the insect body. A second interest, although to the collector and amateur perhaps the dominant one, comes from that recognition of the differences and resemblances among the various insects which is simply the appreciation of kinds, i.e., of species. This interest expanded by oppor¬ tunity and observation and controlled by reason and the habit of order and arrangement is, when extreme, that ardent and much misunderstood and scoffed at but ever-impelling mainspring of the collector and classifier.

2 The Structure and Special Physiology of Insects

Of all entomologists, students of insects, the very large majority are col¬ lectors and classifiers, and of amateurs apart from the few who have “crawl- eries” and aquaria for keeping alive and rearing “ worms” and water-bugs and the few bee-keepers who are more interested in bees than honey, prac¬ tically all are collectors and arrangers. So, as collecting depends on a knowledge of the life of the insect as a whole, and classifying (apart from certain primary distinctions) on only the external structural character of the body, any detailed disquisition on the intimate character of the insec- tean insides would certainly not be welcome to most of the users of this book.

That insects agree among themselves in some important characteristics and differ from all other animals in the possession of these characteristics is implied in the segregation of insects into a single great class of animals- Class here is used with the technical meaning of the systematic zoologist- He says that the animal kingdom is separable into, or, better, is composed of several primary groups of animals, the members of each group possessing in common certain important and fundamental characteristics of structure and function which are lacking, at any rate in similar combination, in all other animals. These primary groups are called phyla or branches. All the minute one-celled animals, for example, compose the phylum Protozoa (the simplest animals); all the starfishes, sea-urchins, sea-cucumbers, and feather-stars, which have the body built on a radiate plan and have no back¬ bone, and have and do not have certain various other important things,, compose the phylum or branch Echinodermata; all the back-boned ani¬ mals and some few others with a cartilaginous rod instead of a bony column along the back compose the class Chordata; all the animals which have the body composed of a series of successive rings or segments, and have pairs of jointed appendages used as feet, mouth-parts, feelers, etc., aris¬ ing from these segments, compose the phylum Arthropoda. There are still other phyla — but I am not writing a zoology. The insects are Arthro¬ poda; and any one may readily see — it is most plainly seen in such forms as a locust, or dragon-fly, or butterfly, and less plainly in the concentrated knobby little body of a house-fly or bee — that an insect’s body shows the characteristic arthropod structure; it is made up of rings or segments, and the appendages, legs for easiest example, are jointed. An earthworm’s body is made up of rings, but it has no jointed appendages. A worm is therefore not an arthropod. A crayfish, however, is made up of distinct successive body-rings, and its legs and other appendages are jointed. And so with crabs and lobsters and shrimps. And the same is true of thousand¬ legged worms and centipeds and scorpions and spiders. All these creatures, then, are Arthropods. But they are not insects. So all the back-boned animals, fishes, amphibians, reptiles, birds, and mammals are Chordates,

The Structure and Special Physiology of Insects 3

but they are not all birds. The phylum Chordata is subdivided into or composed of the various classes Pisces (fishes), Aves (birds), etc. And similarly the phylum Arthropoda is composed of several distinct classes, viz.: the Crustacea, including the crayfishes, crabs, shrimps, lobsters, water-fleas, and barnacles; the Onychophora, containing a single genus (Peripatus) of worm-like creatures; the Myriapoda, including the thousand¬ legged worms and centipeds; the Arachnida, including the scorpions, spiders, mites, and ticks; and finally the class Insecta (or Hexapoda, as it is some¬ times called), whose members are distinguished from the other Arthro-

antennas

pods by having the body-rings or segments grouped into three regions, called head, thorax, and abdomen, by having jointed appendages only on the body- rings composing the head and thorax (one or two pairs of appendages may occur on the terminal segments of the abdomen) , and by breathing by means of air-tubes (trachese) which ramify the whole interior of the body and open on its surface through paired openings (spiracles). The insects also have three pairs of legs, never more, and less only in cases of degeneration, and by this obvious character can be readily distinguished from the Myria¬ pods, which have many pairs, and the Arachnids, which have four pairs. Centipeds are not insects, nor are spiders and mites and ticks. What are insects most of this book is given to showing.

To proceed to the classifying of insects into orders and families and genera and species inside of the all-including class is the next work of the collector and classifier. And for this — if for no other reason — some further knowledge of insect structure is indispensable. The classification rests

4 The Structure and Special Physiology of Insects

mostly on resemblances and differences in corresponding parts of the body, apparent in the various insect kinds. What these parts are, with their names and general characters, and what their particular use and significance are, may be got partly from the following brief general account, and partly from the special accounts given in connection with special groups of insects else¬ where in this book. A little patience and concentration of attention in the reading of the next few pages will make the reader’s attention to the rest of the book much simpler, and his understanding of it much more effective.

The outer layer of the skin or body-wall of an insect is called the cuticle, and in most insects the cuticle of most of the body is firm and horny in char¬

acter, due to the deposition in it, by the cells of the skin, of a substance called chitin. This firm external chitinized * cuticle (Fig. 2) forms an enclosing exoskeleton which serves at once to protect the inner soft parts from injury

FIG . 3. — Bit of body-wall, greatly magnified, of larva of blow-fly, Calliphora erythrocephala, ' to show attachment of muscles to inner surface.

and to afford rigid points of attachment (Figs. 2, 3 and 4) for the many small but strong muscles wdiich compose the insect’s complex muscular system. Insects have no internal skeleton, although in many cases small processes project internally from the exoskeleton, particularly in the thorax or part

* It is not certainly known whether the cuticle is wholly secreted by the skin cells, or is in part composed of the modified external ends of the cells themselves.

The Structure and Special Physiology of Insects 5

of the body bearing the wings and legs. Where the cuticle is not strongly chitinized it is flexible (Fig. 6), thus permitting the necessary movement or play of the rings of the body, the segments of the legs, antennae and mouth-parts, and other parts. The small portions of chitinized cuticle thus isolated or made separate by the thin interspaces or sutures

v.n.'c.

Fig. 4. Fig. 5.

Fig. 4. — Diagram of cross-section through the thorax of an insect to show leg and wing muscles and their attachment to body-wall, h., heart; al.c., alimentary canal; v.n.c. ventral nerve-cord; w., wing; leg; m., muscles. (Much enlarged; after Graber.) Fig. 5. — Left middle leg of cockroach with exoskeleton partly removed, showing muscles. (Much enlarged; after Miall and Denny.)

are called sclerites, and many of them have received specific names, while their varying shape and character are made use of in distinguishing and classifying insects.

Fig. 6. — Chitinized cuticle from dorsal wall of two body segments of an insect, showing sutures (the bent places) between segmental sclerites. Note that the cuticle is not less thick in the sutures than in the sclerites, but is less strongly chitinized (indi¬ cated by its paler color).

The whole body is composed fundamentally of successive segments (Figs. 1 and 7), which may be pretty distinct and similar, as in a caterpillar or termite or locust, or fused together, and strongly modified, and hence dissimilar, as in a house-fly or honey-bee. The segments, originally five or six, composing the head, are in all insects wholly fused to form a single box-like cranium, while the three segments which compose the thorax are in most forms so fused and modified as to be only with difficulty distinguished as originally independent body-rings. On the other hand, in most insects

6 The Structure and Special Physiology of Insects

the segments of the abdomen retain their independence and are more or

prothorax^

labiaMk ■ palpi' ^

proboscis '

\ \ metathorax

\\ mesothorax

Ns ''.coxa

'' trochanter '''"femur

'abdomen

compound eye, antennse.

tarsal segments

Fig. 7. — Body of the monarch butterfly, Anosia plexippus , with scales removed to show external parts. (Much enlarged.)

less similar, thus preserving a generalized or ancestral condition. On the

head are usually four pairs of jointed appendages (Fig. 8), viz., the

antennae and three pairs of mouth-parts,

known as mandibles, maxillae, and labium or

under-lip. Of these the mandibles in most

cases are only one-segmented, while the two

members of the labial pair have fused along

their inner edges to form the single lip-like

labium. The so-called upper lip or lab rum,

closing the mouth above, is simply a fold of

the skin, and is not homologous, as a true

appendage or pair of appendages, with the

other mouth-parts. In some insects with highly

modified mouth structure certain of the parts

may be wholly lost, as is true of the mandibles

of dobson-fly, Corydalis cor- in the case of all the butterflies. The head

nuta, female, showing mouth- bears also the large compound eyes and the

parts, lb., labrum, removed; . 0 ...

md., mandible; mx., maxilla; smaller simple eyes or ocelli (for an account of

li., labium; gl, glossse of la- the eyes see p. 30). Attached to the thorax are

mxf., palpus of maxilla; ant., three Palrs of kgs, whlch are jointed appendages, . antenna. homologous in origin and fundamental struc¬

ture with the mouth-parts and antennae, and two pairs of wings (one or

Fig. 8. — Dorsal asDect of head

The Structure and Special Physiology of Insects 7

both pairs may be wanting) which are expansions of the dorso-laterai skin or body-wall, and are not homologous with the jointed' ventra appendages. The thorax usually has its first or most anterior segmentl the prothorax, distinct from the other two and freely movable, while the hinder two,» called meso- and meta-thoracic segments, are usually ? enlarged and firmly fused to form a box for holding and giving attachment to the numerous strong muscles which move the wings and legs. The abdomen usually includes ten or eleven segments without appendages or projecting processes except in the case of the last two or three, which bear in the female the parts composing the egg-laying organ or ovipositor, or

Fig. 9. Fig. 10.

Fig. 9. — Head, much enlarged, of mosquito, Culex sp., showing piercing and sucking mouth-parts. (After Jordan and Kellogg.)

Fig. 10. — Head and mouth-parts of honey-bee, much enlarged. Note the short, trowel¬ like mandibles for moulding wax when building comb, and the extended proboscis for sucking flower-nectar. (Much enlarged.)

in certain insects the sting, and in the male the parts called claspers, cerci, etc., which are used in mating. On the abdomen are usually specially notice¬ able, as minute paired openings on the lateral aspects of the segments, the breathing-pores or spiracles, which admit air into the elaborate system of tracheae or air- tubes, which ramify the whole internal body (see p. 19).

Of all these external parts two groups are particularly used in schemes of classification because of their structural and physiological importance in connection with the special habits and functions of insect life, and because

8 The Structure and Special Physiology of Insects

of the pronounced modifications and differences in their condition: these are the mouth-parts and the wings.

Insects exhibit an amazing variety in food-habit: the female mosquito likes blood, the honey-bee and butterfly drink flower-nectar, the chinch-bug sucks the sap from corn-leaves, the elm-leaf beetle and maple -worm bite and chew the leaves of our finest shade- trees, the carrion-beetles devour decaying animal matter, the house-fly laps up sirup or rasps off and dissolves loaf- sugar, the nut- and grain-weevils nibble the dry starchy food of these seeds, while the apple-tree borer and timber-beetles find sustenance in the dry wood of the tree- trunks. The biting bird-lice are content with bits of hair and feathers, the clothes- mothi and carpet-beetles feast on our mgs and woolens, while the cigarette-beetle has the depraved taste of our modern youth.

Fig. ii.

Fig. ii. — Mouth-parts, much enlarged, of the house-fly, Musca domestica. mx.p., maxil¬ lary palpi; lb., labrum; li., labium; la., labellum.

Fig. 12. — Head and mouth-parts, much enlarged, of thrips. ant., antenna; lb., labrum; md., mandible; mx., maxilla; mx.p., maxillary palpus; li.p., labial palpus; m.s., mouth-stylet. (After Uzel; much enlarged.)

With all this variety of food, it is obvious that the food-taking parts must show many differences; one insect needs strong biting jaws (Fig. 8), another a sharp piercing beak (Figs. 9, 13, and 14), another a long flexible sucking proboscis (Figs. 10 and 16), and another a broad lapping tongue (Fig. 11). Just this variety of structure actually exists, and in it the classific entomolo¬ gist has found a basis for much of his modern classification.

Throughout all this range of mouth structure the insect morphologists and students of homology, beginning with Savigny in 1816, have been able to trace the fundamental three pairs of oral jointed appendages, the mandi¬ bles, maxillae, and labium. Each pair appears in widely differing condi¬ tions; the mandibles may be large strong jaws for biting and crushing, as with the locust, or trowel-like, for moulding wax, as with the honey-bee, or

Fig. 12.

The Structure and Special Physiology of Insects 9

long, flat, slender, and saw-toothed, as with the scorpion-flies, or needle-like, as in all the sucking bugs, or reduced to mere rudiments or wholly lacking, as in the moths and butterflies. Similarly with the other parts. But by careful study of the comparative anatomy of the mouth structure, and par¬ ticularly by tracing its development in typical species representing the various types of biting, sucking, and lapping mouths, all the various kinds of mouth structure can be compared and the homologies or structural cor¬ respondences of the component parts determined. Figs.. 8 to 16 illustrate

Fig. 13. Fig. 14. Fig. 15.

Fig. 13. — Seventeen-year cicada, Cicada septendecim , sucking sap from twig. (After Quaintance; natural size.)

Fig. 14. — Section of twig of Carolina poplar showing beak of cicada in position when sucking. (After Quaintance; much enlarged.)

Fig. 15. — Mouth-parts, much enlarged, of net-winged midge, Bibicocephala doanei, female, md., mandible; mx., maxilla; mx.l., maxillary lobe; mx.p ., maxillary palpus; li., labium; hyp., hypopharynx; pg., paraglossa of labium; l.ep., labrum and epipharynx.

examples of different mouth structures, with the corresponding parts similarly lettered.

The most conspicuous structural characteristic of insects is their poses- sion of wings. And the wings undoubtedly account for much of the success of the insect type. Insects are the dominant animal group of this age, as far as number of species constitutes dominance, their total largely sur¬ passing that of the species of all the other kinds of living animals. Flight is an extremely effective mode of locomotion, being swift, unimpeded by obstacles, and hence direct and distance-saving, and an animal in flight is safe from most of its enemies. The wings of insects are not modified true appendages of the body, but arise as simple sac-like expansions (Fig. 17) of the body-wall or skin much flattened and supported by a framework of

io The Structure and Special Physiology of Insects

strongly chitinized lines called veins. These veins are corresponding artic¬ ular thickenings, in the upper and lower walls of the flattened wing-sac, which protect, while the wing is forming, certain main tracheal trunks that carry air to the wing- tissue. After the wing is expanded and dry, the tracheae mostly die out, and the veins are left as firm thick- walled branching tubes which serve admirably as a skeleton or framework for the thin membranous wings. It has been found that despite the obvious great variety in the venation, or number and arrange¬ ment of these veins of the wing, a general type- plan of venation is apparent throughout the insect class. The more important and constant veins have been given names, and their branches numbers (Fig. 18). By the use of the same name or number for the corresponding vein throughout all the insect orders, the homologies or morphological correspondences of the veins as they appear in the variously modified wings of the different insects are made apparent. Many figures scattered through this book show the venation of insects of different orders, and the corresponding lettering and numbering indicate the homologies of the veins. As the wing venation presents differing conditions readily noted and described, much use is made of it in classification.

The differences in the wings them¬ selves, that is, in number, relative size of fore and hind wings, and in struc¬ ture, i.e., whether membranous and F i6 delicate, or horny and firm, etc., have

„ , „ . . . . , always been used to distinguish the

tig. io. — Sphinx moth, showing proboscis; J °

at left the proboscis is shown coiled up larger groups, as orders, of insects, on the under side of the head, the nor- and the first classification, that of mal position when not in use. (Large _ . . . .. . . .

figure, one-half natural size; small fig- Linnaeus (l75° aPP*)> divides the class

ure, natural size.) into orders almost solely on a basis

of wing characters. The ordinal names expressed, to some degree, the differences, as Diptera,* two-winged ; Lepidoptera, scale- winged ; Coleoptera, sheath-winged, and so on. As a matter of fact, there may be much differ-

* The derivation of the Linnaean ordinal names is given on p. 223.

The Structure and Special Physiology of Insects 1 1

ence in the wings within a single order; most beetles, for example, have four wings, but some have two and some none. There are indeed wingless species in almost every insect order. But a typical beetle has quite dis¬ tinctive and commonly recognized wing characters; that is, it has two pairs of wings, the fore pair being greatly thickened, and developed to serve as sheaths for the larger, membranous under-pair, which are the true flight wings. Similarly, practically all moths and butterflies have two pairs of

Fig. 17. Fig. 18.

Fig. 17. — Wing of cabbage-butterfly, Pier is rapes, in early sac-like stage, tr., trachea;

tl., tracheoles; l.v., lines of future veins. (After Mercer; greatly magnified.)

Fig. 18. — Diagram of wings of monarch butterfly, Anosia plexippus, showing venation. c costal vein; s.c., subcostal vein; r., radial vein; cu., cubital vein; a ., anal veins. In addition, most insects have a vein lying between the subcostal and radial veins, called the median vein. (Natural size.)

membranous wings completely covered above and below by small scales, which give them their distinctive color and pattern.

The exoskeleton, or cuticle, of the insect body is sometimes nearly smooth and naked, but usually it is sculptured by grooves and ridges, punc¬ tures or projections, and clothed with hairs or those modified flattened hairs known as scales (especially characteristic of butterflies and moths). This clothing of hairs or scales, or the skin itself, is variously colored and pat¬ terned, often with the obvious use of producing protective resemblance or mimicry, but often without apparent significance. (For an account of the colors and patterns of insects and their uses see Chapter XVII.) The hairs may serve for protection, or may be tactile organs, or even organs of hearing (see p. 26). The projecting processes may be spines or thorns or curious and inexplicable

i 2 The Structure and Special Physiology of Insects

knobs and horns. The rhinoceros-beetle (Dynastes) (Fig. 19) and the sacred scarabeus are familiar examples of insects with such prominent processes.

The insect body, as a whole, appears in great variety of form and range of size, as our knowledge of the variety of habit and habitat of insects would lead us to expect. In size they vary from the tiny four-winged chalcids which emerge, after their parasitic immature life, from the eggs of other insects, and measure less than a millimeter in length, to the giant Phasmids

Fig. 19. — Rhinoceros-beetle, Dynastes tityrus, showing chitinous horns.

(walking-sticks) of the tropics, with their ten or twelve inches of body length, and the great Formosan dragon-flies with an expanse of wing of ten inches. A Carboniferous insect like a dragon-fly, known from fossils found at Commentry, France, had a wing expanse of more than two feet. Insects show a plasticity as to general body shape and appearance that results in extreme modifications corresponding with the extremely various habits of life that obtain in the class. Compare the delicate fragility of the gauzy¬ winged May-fly with the rigid exoskeleton and horny wings of the water- beetle; the long-winged, slender-bodied flying-machine we call a dragon¬ fly with the shovel-footed, half-blind, burrowing mole-cricket; the plump, toothsome white ant that defends itself by simple prolificness with the spare, angular, twig-like body of the walking-stick with its effective protective resemblance to the dry branches among which it lives. Compare the leg¬ less, eyeless, antennaless, wingless, sac-like degraded body of the orange- scale with the marvelous specialization of structure of that compact expo¬ nent of the strenuous insect life, the honey-bee; contrast the dull colors of the lowly tumble-bug with the flashing radiance of the painted lady-butterfly. But through all this variety of shape and pattern, complexity and degenera^ tion, one can see the simple fundamental insect body-plan; the successive segments, their grouping into three body-regions, the presence of segmented appendages on head and thorax and their absence on abdomen (except perhaps in the terminal segments), and the modification of these append¬ ages into antennae and mouth-parts on the head, legs on the thorax, and ovipositor, sting, or claspers in the abdomen.

In the character of the structure and functions of the internal organs

The Structure and Special Physiology of Insects i 3

or systems of organs of insects, a special interest attaches to the conditions shown by the circulatory and respiratory systems, and by the special sense-

Fig. 20. — Diagram of lateral interior view of monarch butterfly, Anosia plexippus , show¬ ing the internal organs in their natural arrangement, after the removal of the right half of the body-wall together with the tracheae and fat body; I to III, segments of the thorax; i to 9, segments of the abdomen. Alimentary Canal and Appen¬ dages: ph., pharynx; sd. and sgl., salivary duct and gland of the right side; oe., oesophagus; f.r., food-reservoir; st., stomach; i., small intestine; c.} colon; r.} rec¬ tum; a., anus; m.v., Malpighian tube. Haemal System: h., heart or dorsal vessel; ao., aorta; a.c., aortal chamber; Nervous System (dotted in figure): br., brain; g., suboesophageal ganglion; l.g., compound thoracic ganglia; ag.v ag.4, first and fourth abdominal ganglia. Female Reproductive Organs: cp., copulatory pouch; v., vagina; o., oviduct, and 00., its external opening; r.ov., base of the right ovarian tubes turned down to expose the underlying organs; l.ov., left ovarian tubes in posi¬ tion, and ov.c., their termination and four cords; sp., spermatheca; a.gl. v part of the single accessory gland; a.gl.2, one of the paired accessory glands; only the base of its mate is shown. Head: a., antenna; mx., proboscis; p., labial palpus. (After Burgess; three times natural size.)

organs and their manner of functioning. The muscular system varies from the simple worm-like arrangement of segmentally disposed longitudinal and ring muscles possessed by the caterpillars, grubs, and other worm-like larvae, to the complicated system of such specialized and active forms as the honey-bee and house-fly. Lyonnet describes about two thousand dis¬ tinct muscles in the caterpillar of the goat-moth. Insect muscles are similar, in their finer structure, to those of other animals, most of Fig. 21. — Bit of muscle of a biting bird -louse, them being composed of finely ^urymetopus taurus. (Greatly magnified.)

cross-striated fibers (Figs. 21 and 22) held together in larger or smaller masses and attaching to the rugosities of the inner surface of the exo¬ skeleton. The muscle substance, when fresh, is peculiarly transparent and delicate-looking, but it has great contractile power.

The alimentary canal (Figs. 23-27), like that of other animals, is a tube but little longer than the body in flesh-eating forms, and much longer in plant-feeders; it runs, more or less curving and coiled, through the body from mouth to anal opening, which lies in the last segment of the abdomen.

14 The Structure and Special Physiology of Insects

Fig. 22. — Diagrammatic figures of bits of insect muscle, variously treated. (After Van Gehuchten; greatly magnified.)

contracted elsewhere to be oesophagus or intestine. One or two pairs of salivary glands pour their fluid into the mouth, while the digesting stomach or ventriculus usually possesses two or more pairs of diverticula known as gastric coeca, which are lined with glands believed to secrete special digestive fluids. Neither liver nor kidneys are present in the insect body, but the secretory function of the latter are undertaken by a number of usually long thread-like tubular diverticula of the intestine known as Malpighian tubules. The intestine itself is usually obviously made up of three successive parts, a large intestine, small intestine, and rectum. There are also present not infrequently in¬ testinal coeca.

Two striking peculiarities about the reproductive system of insects are the possession by the female of one or more spermathecae (Fig. 66, r.s.) in which the male fertilizing cells, the spermatozoa, are re¬ ceived and held, and the com¬ pletion of all the envelopes of _ _ .

. .... . Fig. 24. — Dissection of

the egg, including the outer cockroach to show (al.c.)

hard shell, before its specific alimentary canal. (After r Hatschek and Cori: twice

fertilization takes place, r er- natural size )

Fig. 23. — Alimentary canal of a locust. At upper end the oesoph¬ agus, then the ex¬ panded crop, then sev¬ eral large gastric coeca, then the true stomach, the thread-like Malpig¬ hian tubules, the bent intestine, and the ex¬ panded rectum. (After Snodgrass; enlarged.)

The Structure and Special Physiology of Insects 15

tilization is itself accomplished in the lower end of the egg-duct just before the egg is laid, by the escape of spermatozoa from the spermatheca (the female

Fig. 25. — Alimentary canal of larva of harlequin-fly ( Chironomus sp.). oes., oesophagus; s.g., salivary gland; ca., cardiac chamber of stomach; mt., Malpighian tubules; ch., intestinal chamber; si., small intestine; col., colon. (After Miall and Hammond; much enlarged.)

Fig. 26. — Alimentary canal of two species of thrips; at left Trichothrips copiosa, male, at right Aelothrips fasciata. sal.g., salivary gland; oes., oesophagus; prov., proven- triculus; vent., ventriculus; m.t., Malpighian tubules; int., intestine; rec., rectum. (After Uzel; greatly enlarged.)

having of course previously mated) and their entrance into the egg through a tiny opening, the micropyle (Fig. 67), in the egg-shell and inner envelopes. A queen bee mates but once, but she may live for four or five years after this and continue to lay fertilized eggs during all this time. She must

1 6 The Structure and Special Physiology of Insects

receive several million spermatozoa at mating, and retain them alive in the spermath.eca during these after-years.

Fig. 27.— Alimentary canal of dobson-fly, Corydalis cornuta. A, larva; B, adult; C, pupa; oes., oesophagus; prov., proventriculus; g.c., gastric coeca; vent., ventriculus; r.g., reproductive gland; m.t., Malpighian tubules; int., intestine; int.c., intestinal coecum; rec., rectum; drg., oviduct. (After Leidy; twice natural size.)

The circulatory system of insects presents two particular features of inter¬ est in that the blood does not, as in our bodies, carry oxygen to the tissues, and

Fig. 28. — Cross-section and longitudinal section of salivary gland of giant crane-fly, Holorusia rubiginosa. (Greatly magnified.)

that there is a contractile pulsating heart-like organ, but no arteries or veins. The so-called heart is a delicate-walled, narrow, subcylindrical vessel com¬ posed of a series of most commonly from three to eight successive cham¬ bers lying longitudinally along the median line just underneath the dorsal wall of the abdomen and thorax (Figs. 30 and 31). Each chamber opens, guarded by a simple valvular arrangement (Fig. 33), into the chambers

The Structure and Special Physiology of Insects 1 7

behind and before it, the posterior one being closed behind arid the anterior

Fig. 29. — Cells of digestive epithelium of stomach (ventriculus) of crane-fly, Ptychoptera sp., showing secretion of digestive fluids, or expulsion of cell-content. (After Van Gehuchten; greatly magnified.)

one extending forward into or near the head as a narrowed tubular anterior portion, which is sometimes called the aorta. From the anterior open end of this aorta the blood, forced by pulsations of the heart-chambers, which proceed rhythmically from the posterior one forward, pours out into the body-cavity, proceeding in more or less regular cur¬ rents or paths, but never enclosed in arterial vessels, bathing all the tissues, and carrying food to them. Finally taking up fresh supplies of food by bath¬ ing the food-absorbing walls of the alimentary canal, it enters the chambers of the heart through lateral openings in these (either at the middle or anterior end of each), which thus establish communi¬ cation between the body-cavity and heart- The blood receives no more oxygen than it needs for its own use, and thus does not play nearly so complex a function in the insect’s body as in ours. And this simplicity of function probably explains in some degree the extreme primitiveness of the make-up of the circulatory system.

It will be seen that the respiratory system, on the other hand, is particularly highly developed, as it devolves

Fig. 31.

Fig. 30. — Diagram of circulatory system of a young dragon-fly; in middle is the chambered dorsal vessel, or heart, with single artery. Arrows indicate direction of blood- currents. (After Kolbe.)

Fig. 31. — Dissection showing dorsal vessel, or heart, of locust, Dis- sosteira Carolina. (After Snodgrass; twice natural size.)

1 8 The Structure and Special Physiology of Insects

Fig. 32. Fig. 33.

Fig. 32. — Portion of dorsal vessel and pericardial membrane of locust, Dissosteira caro « Una. (After Snodgrass; greatly magnified.)

Fig. 33. — Cross-section of dorsal vessel or heart in pupa of tussock-moth, Hemerocampa leucostigma , showing valves. (Greatly magnified.)

Fig. 34. — Diagram of tracheal system in body of beetle. sp.t spiracles; tr., tracheae. (After Kolbe.)

Fig. 35. — Diagram showing main tracheae in respiratory system of locust, Dissosteira Carolina. (After Snodgrass; twice natural size.)

Fig. 36. — Diagram showing respiratory system in thrips. st.f spiracles. (After Uzel; much enlarged.)

The Structure and Special Physiology of Insects 1 9

on it not merely to take up oxgyen from the outer air and give up the

waste carbon dioxide of the body, but also to convey these gases to and from all the tis¬ sues of the body. The blood is not red, but pale yellowish or greenish, and is really more like the lymph of the ver¬ tebrate body than like its blood

Insects do not breathe through the mouth or any openings on the head, but have a varying number (usually from two to ten pairs) of small paired openings on the Fig. 37. Fig. 38. sides of the thorax and abdo-

FiGo 37. — Diagram showing respiratory system of pupa men. These Openings, called

ol TpTracilsTre « ^des, or stigmata, are ar-

enlarged.) ranged segmentally and in

Fig 38.— Oiagram of tracheae in head of cockroach. most jnsects are t0 be found Note branches to all mouth-parts, and the an¬ tennae. tracheae, or air-tubes. (After Miall on two of the thoracic seg- and Denny.) ments and on all the abdomi¬

nal segments except the last two or three. The openings are guarded by fine hairs or even little valvular lids to prevent the ingress of dust, and are the entrances to an extended system of delicate air-tubes or tracheae which branch and subdivide until the whole of the internal body is reached and ramified by fine capillary vessels bring¬ ing fresh air to all the tissues and carrying off the waste carbon dioxide made by the metabolism of these tissues. The usual general arrangement of this elaborate re¬ spiratory system is shown in Figs. 34, 35, and 36. Short broad trunks lead from each spiracle to a main longitudinal trunk on each side of the body, from which numerous branches arise, these going to particular regions of the body (Fig. 38) Fig. 39. — Piece of trachea (air-tube), and there branching repeatedly until ^

even individual cells get special tiny graph by George O. Mitchell.)

20

The Structure and Special Physiology of Insects

respiratory capillaries. The tracheae are readily recognized under the micro¬ scope by their finely transversely ringed or striated appearance (Fig. 39). These transverse “rings” are really spirally arranged short chitinized thread-like thickenings on the inner wall of the tube, which by their elasticity keep the delicate air-tubes open. The tubes are filled and emptied by a

rhythmic alternately contracting and expanding movement of the abdomen, called the respiratory movement. When the ring-muscles contract, the walls of the abdomen are squeezed in against the viscera, which, compressing the soft air-tubes, force the air out of them through the spiracles; when the body-walls are allowed to spring back to normal position fresh air rushes in through the spiracles and fills up the air-tubes, which expand because of the elastic spiral thickenings in their walls. Insects which live in water either come up to the surface to breathe and in some cases to take down a supply of air held on the outside of the body by a fine pubescence like the pile of velvet, or they are provided with tracheal gills (Fig. 40) which enable them to breathe the air mixed with, or dissolved in, the water. Gilled insects do not, of course, have to come to the surface to breathe. The gills may be thin plate¬ like flaps on the sides or posterior tip of the body, or may be tufts of short thread-like tubes variously arranged over the body. Or they may be, as in the dragon-fly nymphs, thin folds along the inner wall of the rectum, the water necessary to bathe them being taken in and ejected again through the anal opening. In all cases these insect gills differ from those of other animals, as crabs and fishes, in that they are not organs for the purification of the blood, i.e., effecting an exchange of carbon dioxide and oxygen carried by it, but are means for an osmotic exchange of the fresh air dissolved in water for carbon-dioxide-laden air from air-tubes or tracheae which run out into the gills. Probably no more blood enters these gills than is necessary to bring food to them. Impure air is brought to them by air-tubes, and exchanged by osmosis through the thin walls of air-tube and gill-membrane for fresh air, which passes from these gill air-tubes to the rest of the respiratory system of the body.

The nervous system of insects shows the fundamentally segmental make-up of the body better than any of the other systems of internal organs, although probably in the successive chambers of the dorsal vessel or heart, and certainly

Fig. 40. — Young (nymph) of May-fly showing ( g .) tra¬ cheal gills. (After Jenkins and Kellogg.)

The Structure and Special Physiology of Insects 21

in the paired arrangement of the spiracles and tracheal trunks leading from them, a segmental condition is obvious. The central nervous system consists

Fig. 41. — Larva of giant crane-fly, Holorusia rubiginosa. A, entire; B, dissected, show¬ ing all organs except the muscles and ventral nerve-chain, h., head; ant., antenna; i.b.res., imaginal bud of pupal respiratory tube; i.b.wg., imaginal bud of wing; i.b.ms.l., imaginal bud of mesothoracic leg; i.b.h., imaginal bud of balancer; i.b.mt.l. , imaginal bud of metathoracic leg (the imaginal buds of fore legs are con¬ cealed by head-capsule) ; sal.gl., salivary gland (the other salivary gland is removed) ; br., brain; oes., oesophagus; prov., proventriculus; susp., suspensorium ; g.c ., gastric coecum; vent., ventriculus; tr., trachea; ad.tis., adipose tissue; mal.tub., Malpi¬ ghian tubule; d.v., dorsal vessel; w.m., wing-muscles of pericardium; sm.int., small intestine; tes., testis; int.c., intestinal caecum; v.d., vas deferens; Lint., large intestine; sp., spiracle; term.pr., terminal processes. (Twice natural size.)

of a brain and a ventral chain of pairs of ganglia segmentally arranged and connected by a pair of longitudinal cords or commissures (Figs. 42, 43, 44). The two members of each of the pairs of ganglia as well as of the pair of

22 The Structure and Special Physiology of Insects

Fig. 42. Fig. 43.

Fig. 42. — Diagram of ventral nerve-cord of locust, Dissosteira Carolina . (After Snod¬ grass; twice natural size.)

Fig. 43. — Diagram of the nervous system of the house-fly. (After Brandt; much enlarged.)

Fig. 44. — Nervous system of a midge, Chironomus sp. (After Brandt, much enlarged.)

commissures are in most insects more or less fused to form single ganglia and a single commissure, but in others the commissures, at least, are quite distinct. In the simpler or more generalized condition of the nervous system as seen in the simpler insects and the larvae of the higher ones there are from three or four to seven or eight abdominal ganglion pairs, one pair to a segment, a pair in each of the three thoracic segments, and one in the head just under the oesophagus. From this ganglion (or fused pair) circumoesophageal commis¬ sures run up around the oesophagus to an important ganglion (also composed of the fused members of a pair) lying just above the oesophagus and called the brain, or supraoesophageal ganglion (Figs. 45, 46, and 47). From this proceed the nerves to those impor¬ tant organs of special sense situated on the head, the antennae and eyes. From the suboesophageal gan¬ glion nerves run to the mouth-parts, from the thoracic ganglia to the

Fig. 45. — Brain, com¬ pound eyes, and part of sympathetic nerv¬ ous system of locust, Dissosteira Carolina. (After Snodgrass; greatly magnified.)

The Structure and Special Physiology of Insects 23

wings and legs and the complex thoracic muscular system, while from the abdominal ganglia are innervated the abdominal muscles and sting, ovipositor, or male claspers. In addition to this main or ventral nervous system there is a small and considerably varying sympathetic system (Figs. 46 and 48) to which belong a few minute ganglia sending nerves to those viscera which act automatically or by reflexes, as the alimentary canal and heart. This sympathetic system is connected with the central or principal

Fig. 46. — Brain, circumoesophageal commissures, and suboesophageal ganglion of the red-legged locust, Melanoplus jemur-rubrum. oc., ocellus; op.n ., optic nerve; a.n ., antennal nerve; m.oc ., middle ocellus; op. I ., optic lobe; a.l., olfactory lobe; a.s.g ., anterior sympathetic ganglion; p.s.g., posterior sympathetic ganglion; f.g., frontal sympathetic ganglion; Ibr., nerve to labrum; oe.c., circumoesophageal commissure; g\ suboesophageal ganglion; md., nerve to mandible; mx., nerve to maxilla; l.n., nerve to labium; n., unknown nerve, perhaps salivary. (After Burgess; greatly magnified.)

Fig. 47. — Cross-section of brain, oesophagus, circumoesophageal commissures, and suboesophageal ganglion of larva of the giant crane-fly, Holorusia rubiginosa.

nervous system by commissures which meet the brain just at the origin from it of the circumoesophageal commissures.

The specialization of the ventral nerve-chain is always of the nature of a concentration, and especially cephalization of its ganglia (Figs. 49 and 50). The abdominal ganglia may be fused into two or three or even into one compound ganglion; or indeed all of them may migrate forward and fuse with the hindmost thoracic ganglion, thus leaving the whole abdomen

24 The Structure and Special Physiology of Insects

to be innervated by long nerves running from the thorax. The thoracic ganglia may fuse to form one, and in extreme cases all the abdominal and

thoracic ganglia may be fused into one large mid- thoracic center.

In tracing the development of the nervous system during the ontogeny of one of the special¬ ized insects, the changes from generalized condi¬ tion, i.e., presence of numerous distinct ganglia segmentally disposed, shown in the newly hatched

Fig, 49.

Fig. 48. — Part of sympathetic nervous system of larva of harlequin-fly, Chironomus dorsalis, oes., oesophagus; }.g., frontal ganglion; r.n ., recurrent nerve; d.v., dorsal vessel; w4, nerve passing from brain to frontal ganglion (Newport’s fourth nerve); br., brain; rn., point of division of recurrent nerve; tr., tracheae; pg., paired ganglia; d.v.n., nerve of dorsal vessel; d.v.g., ganglia of dorsal vessel; g.n., gastric nerve to cardiac chamber. The course of the recurrent nerve beneath the dorsal vessel is dotted. (After Miall and Hammond; greatly magnified.)

Fig. 49. — Stages in the development of the nervous system of the honey-bee, Apis melli- fica; 1 showing the ventral nerve-cord in the youngest larval stage, and 7 the system in the adult. (After Brandt; much enlarged.)

larva, to specialized condition, i.e., extreme concentration and cephalization, that is, migration forward and fusion of the ganglia, shown in the adult, are readily followed (Figs. 49 and 50).

The special senses of insects and the sense-organs are of particular inter¬ est because of the marked unusualness of the character of the specialization of both the organs and senses, as compared with the more familiar condi¬ tions of the corresponding organs and functions of our body. The world is known to animals only by the impressions made by it on the sense-organs,

The Structure and Special Physiology of Insects 25

and the particular condit'on of functioning of these organs, therefore, is of unique importance in the life of any particular animal. If the senses vary much in their capacities among different animals, the world will have a differ¬ ent seeming to different creatures. It will be chiefly known to any par¬ ticular species through the dominant sense of that species. To the con¬ genitally blind the world is an experience of touched things, of heard things, and of smelled and tasted things. To the bloodhound it is known chiefly by the scent of things. It is a world of odors; the scent of anything deter¬ mines its dangerousness, its desirableness, its interestingness. As insects know it, then, the world depends largely upon the particular character and capacity of their sense-organs, and we realize on even the most superficial examination of the structure of these organs, and casual observation of the

Fig. 50. — Stages in the development of the nervous system of the water-beetle, Mcilius sulcatus ; i showing the ventral nerve-cord in the earliest larval stage, and 7 the system in the adult. (After Brandt; much enlarged.)

responses of insects to those stimuli, like sound-waves, light-waves, dis¬ solved and vaporized substances, which affect the sense-organs, that the insects have some remarkable special sense-conditions. But the difficul¬ ties in the way of understanding the psychology of any of the lower animals are obvious when it is recalled that our only knowledge of the character of sense-perceptions has to depend solely on our experience of our own per¬ ceptions, and on the basis of comparison with this. We do not know if hearing is the same phenomenon or experience with insects as with us. But a comparison of the morphology of the insect sense-organs with that of ours, and a course of experimentation with the sight, hearing, smelling, etc., of insects, based on similar experimentation with our own senses, leads us to what we believe is some real knowledge of the special sense-condi¬ tions of insects.

26 The Structure and Special Physiology of Insects

Insects certainly have the senses of touch, hearing, taste, smell, and sight. If they have others, we do not know it, and probably cannot, as we have

no criteria for recognizing others. The tactile sense resides especially in so-called “ tactile hairs,” scattered more or less abundantly or regu¬ larly over the body. Each of these hairs has at its base a ganglionic nerve-cell from which a fine nerve runs to some body ganglion (Fig. 51). They are specially numerous and conspicuous on the antennae or “ feelers,” and often on certain pro¬ cesses called cerci, projecting from the tip of the abdomen. They may occur, however, on any part of the body, and are usually recognizable by their length and semi-spinous nature. The sense of taste resides in certain small papillae, usually two-segmented, or in certain pits, which

Fig. 51. — Diagram showing innervation of a tactile hair, sh., tactile hair; ch ., chitinized cuticle; hyp., hypoderm, or cellular layer of the skin; s.c., ganglion cell; c.o., gan¬ glion of the central nervous system. (After vom Rath.)

Fig. 52. Fig. 53.

Fig. 52. — Nerve-endings in tip of maxillary palpus of Locusta viridissima. s.h., sense- hairs; s.c., sense-cells; b.c., blood-cells. (After vom Rath; greatly magnified.)

Fig. 53. — Nerve-endings in tip of labial palpus of Machilis polypoda. (After vom Rath; greatly magnified.)

occur on the upper wall of the mouth (epipharynx) and on the mouth- parts, especially the tips of the maxillary and labial palpi, or mouth- feelers. As substances to be tasted have to be dissolved, and have to

The Structure and Special Physiology of Insects 27

come into actual contact with the special taste nerves, it is obvious that insects, to taste solid foods, have first to dissolve particles of these foods in the mouth-fluids, and that the taste-organs have to be situated in the mouth or so that they can be brought into it to explore the food, as are the movable, feeler-like palpi. What experimentation on the sense of taste in insects has been carried on shows that certain insects certainly taste food substances, and indicates that the sense is a common attribute of all insects. Lubbock’s many experiments with ants, bees, and wasps present convincing proof of the exercise of the taste sense by these insects. Forel mixed morphine and strychnine with honey, which ants, attracted by the honey smell, tasted and refused. Will’s experiments show that wasps recognize alum and quinine by taste. He found bees and wasps to have a more delicate gustatory sense than flies.

Smell is probably the dominant special sense among insects. It exists at least in a degree of refinement among certain forms that is hardly equalled elsewhere in the animal kingdom. The smelling organs are micro¬ scopic pits and minute papillae seated usually and especially abundantly on the antennae, but probably also occurring to some extent on certain of the mouth-parts. The fact that the antennae are the principal, and in many insects the exclusive, seat of the olfactory organs has been proved by many experiments in removing the antennae or coating them with par¬ affine. Insects thus treated do not find food or each other. As substances to be smelled must actually come into contact, in finely divided con¬ dition, with the olfactory nerve-element, these pits and papillae are arranged so as to expose the nerve-end and yet protect it from the ruder contact with obstacles against which the antennae may strike. It is certain that most insects find their food by the sense of smell, and the antenna of a carrion-beetle (Fig. 54) shows plainly the special adaptation to make this sense highly effective. On the “leaves” of each antenna of June-beetleS nearly 40,000 olfactory pits occur.

Some of the results of experimentation on smell indicate a delicacy and specialization of this sense hardly conceivable. A few examples will illustrate this. It is believed that ants find their way back to their nests by the sense of smell, and that they can recognize by scent among hundreds of individuals taken from

Fig. 54. — Antenna of a carrion-beetle with the terminal three segments enlarged and flattened, and bearing many smell- ing-pits. (Photomicro¬ graph by George O. Mit¬ chell; much enlarged.)

28 The Structure and Special Physiology of Insects

various communities the members of their own community. Miss Fielde’s experiments show that the recognition of ants by each other depends on the existence of a sense of smell of remarkable differentiative capacity. The odors of the nest, of the species, of the female parent, and of the individ¬ ual are all distinct and perceivable by the smelling-organs, situated on distinct particular antennal segments. In the insectary at Cornell University a few years ago a few females of the beautiful large promethea moth were put into a covered box which was kept inside of the insectary building. No males of this moth species had been seen about the insectary nor in

its immediate vicin¬ ity for several days, although they had been specially sought for by collectors. Yet in a fewT hours after the female moths were first con¬ fined nearly fifty male prometheas were fluttering about outside over the glass roof of the insectary. They could not see the females, but un¬ doubtedly discovered them by the sense of smell. These pro¬ methea moths have elaborately branched or feathered anten¬ nae, affording area for very many smell- ing-pits.

Mayer’s experiments with promethea also reveal the high specialization of the sense of smell. This investigator carried 450 promethea cocoons from Massachusetts to the Florida keys. Here on separated small islands the moths issued from the cocoons, hundreds of miles south of their natural habitat. This isolation insured that no other individuals than those controlled by the experimenter could confuse the observations. Female moths were confined in glass jars with the mouth closed by netting. Other females were confined in smaller glass jars turned upside down and the mouth buried in sand. Males being released at various

Fig. 55. — Auditory organ of a locust, Melanoplus sp. The large clear part in the center of the figure is the thin tym¬ panum with the auditory vesicle (small, black, pear-shaped spot) and auditory ganglion (at left of vesicle and connected with it by a nerve) on its inner surface. (Photomicrograph by George O. Mitchell; greatly magnified.)

The Structure and Special Physiology of Insects 29

Fig. 56. — Male mosquito, showing (a.h.) antennal hairs. (After Jordan and Kellogg; three times natural size.)

distances soon found their way to the jar (containing females) which had its mouth open to the air, but no male came to the jar with its mouth her¬ metically sealed. Through the glass sides of both jars the females were plainly visible. The antennae of certain males were covered with shellac. These males, when released, never found the females, and often paid no attention to them when brought within an inch of their bodies. Of other males the eyes were covered with pitch; but these males had no difficulty whatever in finding the females. It is plainly obvious from these experiments that the males found the females wholly by scent and not at all by sight.

That some insects hear is proved by their posses¬ sion of auditory organs, and has also been demon¬ strated by experiment. The fact, too, that many insects have special sound-making apparatus and do make characteristic sounds is a kind of proof that they can also hear. The auditory organs of insects, curiously enough, are of several kinds and are situated on different parts of the body, in

various species. Among the locusts, katydids, and crickets, the most con¬ spicuous of all the sound-making in¬ sects except the cicada, the ears are small tympanic membranes on the base of the abdomen in the locusts (Fig. 55), and on the tibiae of the fore legs in the katydids and crickets. Associated with each tympanum is a small liquid-filled vesicle and a special auditory ganglion from which an auditory nerve runs to one of the ganglia of the thorax. Among the

Fig. 57.— Diagram of longitudinal section midges and mosquitoes the antennae— through first and second antennal seg- those all-important sensitive structures

lormis, male, showing complex auditory — are abundantly provided with cer- organ composed of fine chitinous rods, tain fine long hairs, the auditory hairs

(After 56), which take up the sound¬

waves and transmit the vibrations to an elaborate percipient structure composed of many fine chitin-rods and ganglion- ated nerves contained in the next to basal antennal segment (Fig. 57). From this segment runs a principal auditory nerve to the brain. Many other insects

nerve-fibers, and nerve-cells. Child; greatly magnified.)

30 The Structure and Special Physiology of Insects

besides the midges and mosquitoes possess this type of auditory organ; in fact such an organ, more or less well developed, has been found in almost every order except the Orthoptera (the order of locusts, crickets, katydids,

etc.) in which the tympanic auditory organs occur. Special isolated hairs scattered sparsely over the body, connected with a special peripheral nervous arrangement, are believed by some entomologists to be a third kind of auditory structure, and are called chordotonal organs. Experimentally the sense of hearing has been surely determined for certain insects. A single striking example of this experimentation must here suffice. Mayer fastened a live male mosquito to a glass slide, put it under a microscope, and had a series of tuning-forks of different pitch sounded. When the Ut4 fork of 512 vibrations per second was sounded many of the antennal hairs were set, sympathetically, into strong vibration. Tuning-forks of pitch an octave lower and an octave higher also caused more vibration than any intermediate notes. The male mosquito’s auditory hairs, then, are specially fitted to respond to, i.e., be stimulated by, notes of a pitch produced by 512 vibrations. Other, but fewer, hairs of different length vibrated in response to other tones. Those auditory hairs are most affected which are at right angles to the direction from which the sound comes. From this it is obvious that, from the position of the antennae and the hairs, a sound will be loudest or most intense if it is directly in front of the head. If the mosquito is attracted by sound, it will thus be brought straight head end on toward the source of the sound. As a

Fig. 58. — Longitudinal sec¬ tion through ocellus of the honey-bee, Apis mellifica. /., cuticular lens; i.c., cell¬ ular layer of skin; c.b., crystalline layer; r.c., ret¬ inal cells; o.n., optic nerve. (After Redikor- zew; greatly magnified.)

Fig. 59. — Ocellar lens of larva of a saw-fly, Cimbex sp., showing its continuity with the chitinized cuticle. (After Redikorzew; greatly magnified.)

matter of fact, Mayer found the female mosquito’s song to correspond nearly to Ut4, and that her song set the male’s auditory hairs into vibration. With little doubt, the male mosquitoes find the females by their sense of hearing.

Insects have two kinds of eyes, simple and compound. On most species both kinds are found, on some either kind alone, and in a few no eyes at all. Blind insects have lost the eyes by degeneration. The most

The Structure and Special Physiology of Insects 3 1

primitive living insects, Campodea and others, have eyes, although only

simple ones. The larvae of the specialized insects, i.e. , those with complete metamor¬ phosis, also have only simple eyes. The com¬ pound eyes are not complex or specialized derivations of the simple ones, but are of in¬ dependent origin and of obviously distinct structural character. The simple eyes, also called ocelli (Fig. 58), which usually occur to the number of three in a little triangle on top of the head, are small and inconspicuous, and consist each of a lens, this being simply a small convexly thickened clear part of the chitinized cuticle of the head-wall (Fig. 59) and a group of modified skin-cells behind it specially provided with absorbent pigment and

Fig. 60. — Part of corneal cuti¬ cle, showing facets, of the compound eye of a horse¬ fly, Therioplectes sp. (Photo¬ micrograph by George O. Mitchell; greatly magnified.)

capable of acting as a simple light-sensitive or retinal surface. The ocellus is supplied with a special nerve from the brain. The compound eyes are always paired and situated usually on the dorso-lateral parts of the head; they are usually large and conspicu¬ ous, sometimes, as in the dragon-flies and horse¬ flies, even forming two-thirds or more of the mass of the head. Externally each compound eye pre¬ sents a number (which varies all the way from a score to thirty thousand) of facets or microscopic polygonal cuticular windows (Fig. 60). These are the cornea of the eye. Behind each facet is a dis¬ tinct and independent subcylindrical eye-element or ommatidium composed of a crystalline cone (want¬ ing in many insects) enveloping pigment (which pre¬ sumably excludes all light-rays except those which fall perpendicularly or nearly so to the corneal lens of that particular ommatidium), and a slender

tapering part including or composed of the nervous Fig. 61. — Longitudinal

or retinal element called rhabdom (Fig. 61). Each section through a few e . • , • . . /" , 1 , facets and eye-elements

of these ommatidia perceives that bit of the external (ommatidia) of the

object which is directly in front of it; i.e., from which compound eye of a

light is reflected perpendicularly to its corneal facet. ™°th* C°cryesfamne

All of these microscopic images, each of a small part cones; p., pigment; r.,

of the external object, form a mosaic of the whole retinal parts ; o.n., optic J nerve. (After Exner;

object, and thus give the familiar name mosaic greatly magnified.)

-on

I .

32 The Structure and Special Physiology of Insects

vision to the particular kind of seeing accomplished by the compound eye.

The character or degree of excellence of sight by the two kinds of eyes obviously varies much. The fixed focus of the ocelli is extremely short,

Fig. 64. Fig. 63.

Fig. 62. — Longitudinal sections through outer part of eye-elements (ommatidia) of com¬ pound eyes of Lasiocampia quercijolia ; ommatidia at left showing disposition of pigment in eyes in the light, at right, in the dark. (After Exner; greatly magnified.) Fig. 63. — Longitudinal section through a few eye-elements of the compound eye of Cato- cola nupta; left ommatidia taken from an insect killed in the dark, right ommatidium taken from insect killed in the light. (After Exner; greatly magnified.)

Fig. 64. — Section through the compound eyes of a male May-fly, showing division of each compound eye into two parts, an upper part containing large eye -elements (ommatidia), and a lower part containing small eye-elements (ommatidia). (After Zimmerman ; greatly magnified.)

and probably the range of vision of these eyes is restricted to an inch or two in front of the insect’s head. Indeed entomologists commonly believe that the ocelli avail little beyond distinguishing between light and darkness. With the compound eyes the focus is also fixed, but is longer and the range of vision must extend to two or three yards. It is obvious that the larger

The Structure and Special Physiology of Insects 33

and more convex the eyes the wider will be the extent of the visual field, while the smaller and more abundant the facets the sharper and more dis¬ tinct will be the image. Although no change in focus can be effected, cer¬ tain accommodation or flexibility of the seeing function is obtained by the movements of the pigment (Figs. 62 and 63) tending to regulate the amount of light admitted into the eye (as shown by Exner) , and by a difference in size and pigmental character of the ommatidia (Fig. 64) composing the com¬ pound eyes of certain insects tending to make part of the eye especially

Fig. 65. — A section through the compound eye, in late pupal stage, of a blow-fly, Calli- phora sarracenice. In the center is the brain with optic lobe, and on the right-hand margin are the many eye-elements (ommatidia) in longitudinal section. (Photomi¬ crograph by George O. Mitchell; greatly magnified.)

adapted for seeing objects in motion or in poor light, and another part for seeing in bright light and for making a sharper image (as shown by Zim¬ merman for male May-flies, and by myself for certain true flies (see p. 318)). Our careful studies of the structure of the insect eye, and the experimentation which we have been able to carry on, indicate that, at best, the sight of insects cannot be exact or of much range.

The psychology of insects, that is, their activities and behavior as deter¬ mined by their reflexes, instincts, and intelligence, is a subject of great inter¬ est and attractiveness, but obviously one difficult to study exactly. The

34 The Structure and Special Physiology of Insects

elaborateness of many insect instincts, such as those of the ants, wasps, and bees, to choose examples at once familiar and extreme in their complexity, makes it very difficult to analyze the trains of reactions into individual ones, and to determine, if it is indeed at all determinable, the particular stimuli which act as the springs for these various reactions. The attitude of the modern biologist in this matter would be to keep first in mind the theory of reflexes, to look keenly for physico-chemical explanations of the reac¬ tions, and only when forced from this position by the impossibility of find¬ ing mechanical explanations for the phenomena to recognize those com¬ plex reflexes which we call instincts, and finally those acts which we call intelligent, or reasonable, and which are possible only to the possessors of associative memory. The investigations, mostly recent, which have been directed toward a determination of the immediate springs or stimuli of insect reactions indicate clearly that many of these responses, even some which were formerly looked on as surely indicative of considerable intelli¬ gence on the part of their performers, are explicable as rigid reflex (mechan¬ ical) reactions to light, gravity, the proximity of substances of certain chemical composition, contact with solid bodies, etc. On the other hand the position of the extreme upholders (Bethe, Uexkull, and others) of the purely reflex explanation of all insect behavior will certainly prove untenable. As one of the phases of insect biology to which this book is particularly devoted is that which includes the study of habits, activities, or behavior, we may dispense with any special discussion of instinct in this introductory chapter. It is sufficient to say that no other class of invertebrate animals presents such an interesting and instructive psychology as the insects.

ifi

CHAPTER II

DEVELOPMENT AND META¬ MORPHOSIS

HAT animals are born or hatch from eggs in an immature condition is such familiar natural history that we are likely to overlook the significance and consequences of the fact unless our attention is particularly called to them. This condition of immaturity makes it necessary that part of the free life of the organism has to be devoted to growth and development and has to be undergone in an imperfect condition, a condition of structure and physiology, indeed, which may be very different from that of the parents or of maturity. While most animals that are born alive re:emble the parents in most respects, always excepting that of size, many of those animals which hatch from eggs deposited outside the body of the mother issue from the egg with few indeed of the characteristics of the parents and may be so dissimilar from them that only our knowledge of the life-history of the animal enables us to recognize these young individuals as of the same species as the parent. The butterfly hatching as the worm¬ like caterpillar, and the frog as the fish-like tadpole, are the classic examples of this phenomenon. The mammals, our most familiar examples of animals which give birth to their young alive and free, nourish, for weeks or months before birth, the developing growing young. But with egg-laying animals usually only such nourishment is furnished the young as can be enclosed as food-yolk within the egg-shell. As a matter of fact, some young which hatch from eggs, as, for example, chickens, quail, etc., hatch in well- developed condition; and some young mammals, nourished by the mother’s body until birth, are in a conspicuously undeveloped state, as a young kangaroo or opossum. But nevertheless it is generally true that an animal hatched from an egg has still a larger amount of development to undergo before it comes to the stature and capacity of its parents than one which is

35

36

Development and Metamorphosis

born alive, after having passed a considerable time growing and developing in the body of the mother. And this difference in degree of development at birth is largely due simply to the difference in amount of nourishment which can be afforded the young. The embryo in the egg uses up its food early in its developmental career and before it has reached the stage of likeness to its parents. It issues in a condition picturing some far-distant ancestor of its species, or more frequently, perhaps, in a modified, adapted condition, fit to make of this tender unready creature thus thrust before its time into the struggle for living an organism capable of caring for itself, although not yet endowed with capacities as effective as, or even similar to, those of the parent.

It is familiar to us, then, that development is not wholly postnatal or postembryonic ; that before birth or hatching a greater or less amount of

development, requiring a longer or shorter period of time, has already been undergone. Every animal begins life as a simple cell; all animals except the Protozoa (the simplest ani¬ mals, those whose whole body for its whole life is but a single cell) finish life, if red Nature permits them to come through myriad dangers safely to maturity, as a complex of thousands or millions of cells united into great variety of tissues and organs. This great change from most simple to most complex condition constitutes development: the actual increase of body-matter and extension of dimensions is growth.

Most insects hatch from eggs; being bom alive is the exceptional experience of the young of but few kinds, and even this is a sort of pseudo-birth. Such hatch alive, one may better say, for they begin life in eggs, not laid out¬ side the mother body to be sure, but held in the egg-duct until hatching-time. With very few exceptions, young insects are not nourished by the mother except in so far as she stores a supply of yolk around or by the side of each embryo inside the egg-shell. The form¬ ing of the egg is a matter which does not lend itself readily to the observa¬ tion and study of amateurs, but is a phenomenon of unusual interest to whomever is privileged to discover it. The insect ovaries consist of a pair of little compact groups of short tapering tubes (Fig, 66). In the anterior or beginning end of each tube is a microscopic space or chamber from whose walls cells loosen themselves and escape into the cavity. These cells become

Fig. 66. — Ovaries and oviducts of a thrips. o.t., ovarial tubes; o.d., oviduct; r.s., seminal receptacle, or spermatheca; d.r.s., duct of the seminal re¬ ceptacle. (After Uzel; much enlarged.)

Development and Metamorphosis

37

either the germinal or the food part of the eggs. There seems to exist no differentiation among these cells at first, but soon certain ones begin to move slowly down through the egg-tube in single file, each becoming sur¬ rounded and enclosed by yolk, i.e., reserve foodstuff. This gathering of yolk increases the size of the forming eggs, so that they appear as a short string of beads of varying size enclosed in the elastic egg-tube. When of considerable size each egg in the lower end of the tube becomes enclosed

Fig. 67. — Insect eggs and parts of eggs, showing micropyle. a, egg of Drosophila cel- laris; b, upper pole of egg of robber-fly, Asilus crabriformis ; c, upper pole of egg of hawk -moth, Sphinx populi; d, egg of head-louse, Pediculus capitis; e, egg of dragon-fly, Libellula depressa ; f, upper surface of egg of harpy-moth, Harpyia vinula; g, upper pole of egg of Hammalicherus cerdo; h, upper pole of egg of sul¬ phur-butterfly, Colias hyale. (After Leuckart; much enlarged.)

in two envelopes, a membranous inner one (yolk or vitelline membrane) and an outer horny one, the chorion or egg-shell. But both of these envelopes are pierced at one pole by a tiny opening, the micropyle (Fig. 67), and through this opening the fertilizing spermatozoa enter the egg from the seminal receptacle just before the egg is extruded from the body.

The development of the embryo within the egg is also securely sealed away from the eyes of most amateurs. The study of insect embryology requires a knowledge of microscopic technic, and facilities for fixing and

38 Development and Metamorphosis

imbedding and section-cutting which are not often found outside the college laboratory. But the particularly interesting and suggestive stages in this development may be outlined and illustrated in brief space. First, the germinal cell near the center of the egg divides repeatedly (Fig. 68 A) and the resulting new cells migrate outward against the inner envelope of the egg and arrange themselves here in a single peripheral layer, called the blastoderm (Fig. 68 D , bl). On what is going to be the ventral side of the egg the cells of the blastoderm begin to divide and maSs themselves to form the ventral plate (Fig. 69 C). The embryo is forming here; the rest of the blastoderm becomes modified and folded to serve as a double membranous envelope (called amnion and serosa) for the embryo. Stretching nearly from pole to pole as a narrow streak along the ventral aspect of the egg, the

A B C o

Fig. 68. — Early stage in development of egg of water-scavenger beetle, Hydrophilus sp. A, first division of nucleus; B, migration of cleavage -cells outward; C, beginning of blastoderm; D, blastoderm; y., yolk; dc., cleavage -cells; yc., yolk-cells; hi., blastoderm. (After Heider; greatly magnified.)

developing embryo begins soon to show that fundamental structural charac¬ teristic of insects, a segmental condition (Fig. 69 D). One can now make out the forming body-rings or segments, and each soon shows the beginnings or rudiments of a pair of appendages (Fig. 69 E). The appendages of the head and thoracic segments continue to develop and begin soon to assume their definitive character of antennae, mouth-parts, and legs, but those of the abdominal segments never get farther than a first appearance and indeed soon disappear. In the mean time the internal systems of organs are grad¬ ually developing, the ventral nerve-chain first, then the alimentary canal, and later the muscles, tracheae, and the heart. All the time the yolk is being gradually used up, fed on, by the cells of the developing and growing embryo, until finally comes the disappearance of all the stored food, and the time for hatching.

Development and Metamorphosis

39

The eggs have been laid, because of the remarkable instinct of the mother, in a situation determined chiefly by the interests of the young which are to hatch from them. The young of many kinds of insects take very different food from that of the mother — a caterpillar feeds on green leaves, the butterfly on flower-nectar — or live under very different circum¬ stances — young dragon-flies and May-flies live under water, the adults in the air. A monarch butterfly, which does not feed on leaves, nor has ever before produced young, seeks out a milkweed to lay its eggs upon. The young monarchs, tiny black-and-white-banded caterpillars, feed on the

Fig. 69. — Early stages in the development of the egg of saw-fly, Hylotoma beriberidis. C, ventral plate removed from egg; D, ventral plate, showing segmentation of body; E, embryo, showing developing appendages; F, same stage, lateral aspect; G, older stage, lateral aspect, ant., antenna; md., mandible; mx., maxilla; li., labium; ll , l2, P, legs; sg., salivary glands; st., spiracles; ab.ap., abdominal appendages; n.c., nerve- centers; a., anal opening; lb., labrum; sd., oesophageal invagination; y., yolk; b.s., abdominal segments; pd., intestinal invagination; am., amnion; s., serosa. (After Graber; greatly magnified.)

green milkweed leaf- tissue; indeed they starve to death if they cannot have leaves of precisely this kind of plant! The reason that the butterfly, whose only food is the nectar of almost any kind of flower, ranges wide to find a milkweed for its eggs, is one not founded on experience or teaching or lea- son, but on an inherited instinct, which is as truly and as importantly an attribute of this particular species of butterfly as its characteristic color pattern or body structure. And the female of the great flashing strong¬ winged dragon-fly, queen insect of the air, when egg-laying time comes, feels a strange irresistible demand to get these eggs into water, dropping them in from its airy height, or swooping down to touch the tip of the abdo-

4°

Development and Metamorphosis

men to the water’s surface, there releasing them, or even crawling down some water-plant beneath the surface and with arduous labor thrusting the eggs into the heart of this submerged plant-stem. From the eggs hatch wingless dwarf-dragons of the pond bottom, with terrible extensile, clutch¬ ing mouth-parts and an insatiable hunger for living prey.

So our young insects, after completing their embryonic development, come to the time of their appearance as free individuals compelled to find their own food and no longer sheltered by a firm egg-shell from the strenu-

Fig. 70. — Series of stages in development of egg of fish-moth, Lepisma sp. A, begin¬ ning embryo; B, embryo showing segmentation; C, embryo showing appendages; D, embryo more advanced; E , embryo still more advanced; F, embryo still older and removed from egg; G, embryo removed from egg at time of readiness to hatch. y., yolk; emb., embryo; ser ., serosa; am., amnion; ant., antenna; lb., labrum; md., mandible; mx., maxilla; mx.p., maxillary palpus; li., labium; li.p., labial palpus; ll, l2, P, legs; pr., proctodaeum, or intestinal invagination; cer., cerci; mp., middle posterior process. (After Heymons; greatly magnified.)

ous fighting and hiding of the open road. Now these young insects, depend¬ ing upon how far they have carried their developmental course in the egg, hatch either almost wholly like their parents (excepting always in size), or in a condition fairly resembling the parents, but lacking all traces of wings and showing other less conspicuous dissimilarities, or finally they may appear in guise wholly unlike that of their parents, in such a condition indeed that they would not be recognized as insects of the same kind as the parents. But in all cases the young are certain, if they live their allotted days or weeks

Development and Metamorphosis

4i

or months, to attain finally the parent structure and appearance. This attainment is a matter of further development, of postembryonic develop¬ ment, and the amount or degree of this development or change is obviously determined by the remoteness or nearness of the young at the time of hatch¬ ing to the adult or parental condition. The young of many of our most familiar insects, as beetles, flies, moths and butterflies, and ants, bees, and wasps, hatch out extremely unlike their parents in appearance: the well- known worm-like caterpillars of butterflies and moths are striking examples of this unlikeness. The changes necessarily undergone in the develop¬ ment from caterpillar to butterfly are so great that there actually results a very considerable degree of making over, or metamorphosis of the insect, and for convenience of roughly classifying insects according to their develop¬ ment, entomologists have adopted the terms complete metamorphosis, incomplete metamorphosis, and no metamorphosis to indicate three not very sharply distinguished kinds or degrees of postembryonic development.

In the latter category are comparatively few species, because most insects have wings, and no insect is winged at birth. But the members of the sim¬ plest order (Aptera) are all primitively wingless, and their young are, in practically all particulars except body size and the maturity of the reproductive glands, like the adults (Fig. 71) ; their development may fairly be said to take place without metamorphosis. In addition to these primitively simple insects there are certain degenerate wingless species like the biting bird-lice, for example, whose young also reach the parental stature and character without meta¬ morphosis.

In the next category, that of development with in¬ complete metamorphosis, are included two large orders

of insects and several smaller ones. All the sucking-bugs fig. 71. _ Young

(order Hemiptera) and all the locusts, katydids, crickets, and cockroaches (composing the order Orthoptera), as well as the May-flies, dragon-flies, white ants, and several other small groups of unfamiliar forms, agree in having their young hatched in a condition strongly resembling the parents, although lacking wings, and in some cases, particu¬ larly those in which the young live on different food and in a different habitat from the adults, differing rather markedly in several superficial characters. Such is the case, for example, with the dragon-flies, whose young are aquatic and breathe by means of tracheal gills, and are provided with specially con¬ structed seizing and biting mouth-parts. But in such essential character¬ istics as number of legs, character of eyes and antennae, and, usually, char¬ acter of mouth-parts, the young and parent agree. During postembryonic

and adult of Po- dura sp., one of the simplest in¬ sects, showing development without meta- morphosis. (Much enlarged.)

42

Development and Metamorphosis

Fig. 72. — Developing stages, after hatching, of a locust, Melanoplus femur-rubrumt a, just hatched, without wing-pads; b, after first moulting; c, after second moulting, showing beginning wing-pads; d, after third moulting; e , after fourth moulting, /, adult with fully developed wings. (After Emerton; younger stages enlarged; adult stage, natural size.)

Fig. 73. — Stages in development of the wings of a locust. /., developing rudiment of fore wing; h., developing rudiment of hind wing; w„ wing-pad. (After Graber; twice natural size.)

Development and Metamorphosis 43

development the young have to develop wings and make what other change is necessary to reach the adult type, but the life is continually free and active and the change is only a simple gradual transformation of the various parts in which differences exist. A common locust is an excellent example of an insect with such incomplete metamorphosis. Fig. 72 shows the develop¬ ing locust at different successive ages, or stages, as these periods are called because of their separation from each other by the phenomenon, common to all insects, of moulting. As the insect grows it finds its increase of girth and length restrained by the firm inelastic external chitinized cuticle, or exoskeleton. So at fixed periods (varying with the various species both in number and duration) this cuticle is cast or moulted. From a median longitudinal rent along the dorsum of the thorax and head, the insect, soft and dangerously helpless, struggles out of the old skin, enclosed in a new cuticle which, however, requires some little time to harden and assume its proper colors (often protective).

After each moulting the young locust appears markedly larger and with its wing-pads better developed (Fig. 73). But not until the final moulting — in the case of the locust this is the fifth — are the wings usable as organs of flight. So that there is after all likely to be a rather marked difference between the habits of the young and those of the adult of an insect with incomplete metamor¬ phosis, that difference being primarily due to structural differences. The young are confined to the ground, and their locomotion is limited to walking or hopping. The adults can live, if they like, a life in the air, and they have a means of locomotion of greatly extended capability.

The insects with complete metamorphosis are the beetles, the two¬ winged flies, the butterflies and moths, the ichneumons, gall-flies, ants, bees, and wasps, the fleas, the ant-lions, and several other small groups of insects with less familiar names. In the case of all the thousands of species in these groups, the young when hatched from the egg differ very much in structure and appearance, and also in habits and general economy, from the parents. Familiar examples of such young are the caterpillars and “ worms” of the moths and butterflies, the grubs of beetles, the mag-

Fig. 74. — Metamorphosis, incomplete, of an assassin-bug (family Reduviidae, order Hemiptera). A, young just hatching from eggs; B, young after first moulting, showing beginning wing-pads; C, older stage with complex wing-pads; D, adult with fully developed wings. (One-half larger than natural size.)

44

Development and Metamorphosis

gots of the flesh- and house-flies, and the helpless soft white grubs in the cells of bees and wasps. These strange young, so unlike their parents, have the generic name larvae, and the stage or life of the insect passed as a larva is known as the larval stage. In almost all cases these larvae have mouth-parts fitted for biting and chewing, while most of the adults have sucking-mouth parts; the larvae have only simple eyes and small inconspicu-

Fig. 75. — Metamorphosis, complete, of monarch butterfly, Anosia plexippus. a, egg (greatly magnified); b, caterpillar or larva; c , chrysalid or pupa; d, adult or imago. (After Jordan and Kellogg. Natural size.)

ous antennae; the adults have both simple and compound eyes and well- developed conspicuous antennae; the larvae may have no legs, or one pair or two or any number up to eight or ten pairs; the adults have always three pairs; the larvae are wholly wingless, nor do external wing-pads (i.e., developing wings) appear outside the body during the larval stage; the adults have usually two pairs (sometimes one or none) of fully developed wings. Internally the differences are also great. The musculation of the

Development and Metamorphosis

45

larva is like that of a worm, to accomplish wriggling, crawling, worm-like locomotion; in the adult it is very different, particularly in head and thorax; the alimentary canal is usually adapted in the larva for manipulating and digesting solid foods; in the adult, usually (except with the beetles and a few other groups), for liquid food; there may be large silk-glands in the larva, which are rarely present in the adult; the respiratory system of the larvae of some flies and Neuroptera is adapted for breathing under water; this is only rarely true of the adults. The heart and the nervous system show lesser dif¬ ferences, but even here there is no iden¬ tity : the ventral nerve chain of the larvae may contain twice as many distinct gan¬ glia as in the adult.

The larva lives its particular kind of life: it grows and moults several times; but externally it shows at no time any more likeness to the adult than it did at hatching. But after its last moult it ap¬ pears suddenly in the guise of a partially formed adult in (usually) quiescent mummy-like form, with the antennae, legs, and wings of the adult folded compactly on the under side of the body, and the only sign of life a feeble bending of the hind-body in re¬ sponse to the ' stimulus of a touch. This is the insect of complete meta¬ morphosis in its characteristic second stage (or third if the egg stage

is called first), the pupal stage. The mummy is called pupa or chrysalid. As the insect cannot, in this stage, fight or run away from its enemies, its defence lies in the instinctive care with which the larva, just before pupation, has spun a protecting silken cocoon about itself, or has burrowed below the surface of the ground, or has concealed itself in crack or crevice. Or the defence may lie in the fine harmonizing of the color and pattern of the naked exposed chrysalid with the bark or twig on which it rests; it may be visible but indistinguishable. The insect as pupa takes no food; but the insect as larva has provided for this. By its greed and overeating it has laid up a reserve or food-store in the body which is drawn on during the pupal stage and carries the insect through these days or weeks or months of waiting for the final change, the transformation to the renewed,

Fig. 77. — Adult worker (a) and larva ( b ) of honey-bee. (Adult natural size; larva twice natural size.)

Fig. 76. — Larva, pupa, and adult of the flesh-fly, Calliphora erythroce- phala , with complete metamor¬ phosis. (Two times natural size.)

46

Development and Metamorphosis

active food-getting life of the adult or imaginal stage. Familiar examples of this kind of metamorphosis, the real metamorphosis, are provided by the life of the monarch butterfly, the honey-bee, and the blow-fly. The great red-brown monarch lays its eggs on the leaves of a milkweed; from the eggs hatch in four days the tiny tiger-caterpillars (larvae) (Fig. 75) with biting mouth-parts, simple eyes, short antennae, and eight pairs of legs on its elon¬ gate cylindrical wingless body. The caterpillars bite off and eat voraciously bits of milkweed-leaf; they grow rapidly, moult four times, and at the end of eleven days or longer hang themselves head downward from a stem or

Fig. 78. — Brood-cells from honey-bee comb showing different stages in the metamor¬ phosis of the honey-bee; worker brood at top and three queen-cells below; begin¬ ning at right end of upper row of cells and going to left, note egg, young larva, old larva, pupa, and adult ready to issue; of the large curving queen-cells, two are cut open to show larva within. (After Benton; natural size.)

leaf and pupate, i.e., moult again, appearing now not as caterpillars, but as the beautiful green chrysalids dotted with gold and black spots. The form¬ ing antennal legs and wings of the adult show faintly through the pupal cuticle, but motionless and mummy-like each chrysalid hangs for about twelve days, when through a rent in the cuticle issues the splendid butterfly with its coiled-up sucking proboscis, its compound eyes, long antennae, its three pairs of slender legs (the foremost pair rudimentary), and its four great red-brown wings. The queen honey-bee lays her eggs, one in each of the scores of hexagonal cells of the brood-comb (Fig. 78). From the egg there hatches in three days a tiny footless, helpless white grub, with biting mouth- parts and a pair of tiny simple eyes. The nurses come and feed this larva steadily for five days; then put a mass of food by it and “cap” the cell; the larva has grown by this time so as nearly to fill the cell. It uses up the stored food, and “changes” to the pupa, with the incomplete lineaments of the adult bee. It takes no more food, but lies like a sleeping prisoner

Development and Metamorphosis

47

in its closed cell for thirteen days, and then it awakens to active life, gnaws its way through the cell-cap and issues into the hive-space a definitive honey¬ bee with all the wonderful special structures that make the honey-bee body such an effective little insectean machine. The blow-fly (Fig. 76) lays a hun¬ dred or more little white eggs on exposed meat. From these eggs come in twenty or thirty hours the tiny white wriggling larvae (maggots) , footless, eye¬ less, wingless, nearly headless, with a single pair of curious extensile hooks for mouth-parts. For ten to fourteen days these larvae squirm and feed and grow, moulting twice in this time; they then pupate inside of the larval cuticle, which becomes thicker, firmer, and brown, so as to enclose the deli¬ cate pupa in a stout protective shell. The blow-fly now looks like a small thick spindle-shaped seed or bean, and this stage lasts for twelve or fourteen

Fig. 79. — Dipterous larvae showing (through skin) the imaginal discs or buds of wings, these buds being just inside the skin. A, larva of black fly, Simulium sp.; B, anterior end of larva of midge, Chironomus sp.; C, anterior end, cut open, of larva of giant crane-fly, Holorusia rubiginosa ; h.pr., bud of prothoracic respiratory tube; h.pl. , bud of prothoracic leg; h.mw., bud of mesothoracic wing; h.rnl., bud of mesothoracic leg; h.mtb., bud of metathoracic balancer; h.mtl., bud of metathoracic leg. (Much enlarged.)

days. Then the winged imago, the buzzing blow-fly, as we best know it, breaks its way out. In the house-fly the same kind of life-history, with complete metamorphosis of the extremest type, is completed in ten days. Nor do we realize how really extreme and extraordinary this metamorpho¬ sis is until we study the changes which take place inside the body, as well as those superficial ones we have already noted.

The natural question occurs to the thoughtful reader: “Is the meta¬ morphosis or transformation in the postembryonal development of such insects as the butterfly, bee, and blow-fly as sudden or discontinuous and as radical as the superficial phenomena indicate? ” The answer is no, and yes; the metamorphosis is not so discontinuous or saltatory and yet is even more radical and fundamental than the external changes suggest. To

48

Development and Metamorphosis

take a single example, the case of the blow-fly (admittedly an extreme one), the phenomena of internal change are, put briefly, as follows: The imaginal wings, legs, and head-parts begin to develop as deeply invaginated little buds of the cell-layer of the larval skin early in larval life. This develop¬ ment is gradual and continuous until pupation, when the wing and leg rudi-

Fig. 8o. — Stages in development of wing-buds in the larva of the giant crane-fly, Holorusia rubiginosa (the wing-buds have been dissected out and sectioned, so as to show their intimate anatomy). A, B, C, D, four stages successively older: ch., chitinized cuticle; hyp., hypoderm or cellular layer of skin; tr., trachea; trl tracheoles; p.m., peritrophic membrane; w., developing wing; t.v tracheal branch indicating position of future wing-vein. (Greatly magnified.)

ments and the new head are pulled out upon the exterior of the body. Just before pupation, when the larva has given up its locomotion and feeding, the larval muscles, tracheae, salivary glands, alimentary canal, and some other tissues begin to disintegrate, and rapidly break wholly down, so that in the pupa there appear to be no internal organs except the nervous system, reproductive glands, and perhaps the heart, but the whole interior of the

Development and Metamorphosis

49

body is filled with a thick fluid in which float bits of degenerating larval tissue. At the same time with this radical histolysis or breaking down of tissue a rapid histogenesis or developing of imaginal parts from certain groups of undifferentiated primitive cells, derived probably mostly from the larval skin-cells, is going on. Thus many of the larval organs and tissues, instead of going over into the corresponding imaginal ones, wholly disinte¬ grate and disappear, and the imaginal parts are newly and independently derived. In connection with the breaking down of the larval tissues phagocytes or freely moving, tissue¬ eating, amoeboid blood-cells play an important part, although one not yet fully understood. They are either the causal agents of the histolysis, or are assisting agents in it, the tissue disintegration beginning independently, or — a recent sugges¬ tion — they are perhaps more truly to be looked on as trophocytes, that is, carriers of food, namely, disintegrating tissue, to the develop¬ ing centers of the imaginal parts.

Much investigation remains to be done on this interesting subject of histolysis and histogenesis in insects with complete metamor¬ phosis, but enough has been already accomplished to show the basic and extreme character of the transformation from larva to adult.

If we ask for the meaning of such unusual and radical changes in the development of insects, we confront at once an important biological prob¬ lem. Most biologists believe that in a large and general way the develop¬ ment of animals is a swift and condensed recapitulation of their evolution; meaning by development the life-history or ontogeny of an individual, and by evolution the ancestral history or phylogeny of the species. According to this “biogenetic law” the interpretation of the significance of the various stages and characters assumed by an animal in the course of its development from single fertilized egg-cell to the complex many-celled definitive adult stage is simple: These stages correspond to various ancestral ones in the long genealogical history of the species. Every vertebrate, for example, is at some period in its development more like a fish than any other living kind of animal ; it has gill-slits in its throat, is tailed, and is indeed a fish¬ like creature. This is its particular developmental stage, corresponding

Fig. 8 i. — A cross section of the body of the pupa of a honey-bee, showing the body-cavity filled with disintegrated tissues and phago¬ cytes, and (at the bottom) a budding pair of legs of the adult, the larvae being wholly legless. Photomicrograph by George O. Mitchell; greatly magnified.)

5°

Development and Metamorphosis

to the ancestral fish-like ancestors of all vertebrates. Do then the larvae and pupae of insects with complete metamorphosis represent ancestral stages in insect evolutionary history? In some degree the larval stage does, but

in no degree does the pupal. Insects are certainly not de¬ scended from an animal that, like a pupa, could neither move nor eat and which had no in¬ ternal organs except a nervous system, heart, and rudimentary reproductive glands. Biologists recognize that the exigencies of life during adolescence may profoundly modify what might be termed the normal course of development. As long as the developing animal is shielded from the struggle for existence, is provided with a store of food and protected from enemies by lying in an egg-shell or in the body of the mother, it may pursue fairly steadily its reca¬ pitulatory course of development; but once emerged and forced to shift for

Fig. 82. — A bit of degenerate muscle from tussock- moth, Hemerocampa leucostigma. Note phago¬ cytic cells attacking muscle at the margins. (Greatly magnified.)

Fig. 83. — Degenerating muscle from pupa of giant crane-fly, Holorusia rubiginosa, show¬ ing phagocytic cells penetrating and disintegrating the muscle -tissue. (Greatly magnified.)

itself, it must be, at whatever tender age it is turned out, or whatever ancient ancestor it is in stage of simulating, adapted to live successfully under the present-day and immediate conditions of life. If the butterfly gets hatched long before it has reached its definitive butterfly stage, and while it is in a stage roughly corresponding to some worm-like ancestors — and from such ancestors insects have undoubtedly descended — it must be fitted to live

Development and Metamorphosis 51

successfully a crawling, squirming, worm-like life. That those insects which hatch as worm-like larvae do in fact owe their wingless, worm-like body con¬ dition partly to being born in a stage simulating a worm-like ancestor is proba-

Fig. 84. — Degeneration, without phagocytosis, of salivary glands in old larva of giant crane-fly, Holorusia rubiginosa. A, cross-section of salivary gland before degen¬ eration has begun; B , cross-section of salivary gland after degeneration has set in. (Greatly magnified.)

bly true. But to be a successful worm demands very different bodily adapta¬ tions from those of a successful butterfly. And so far does the larval butterfly go, or so far has it been carried, in meeting these demands that nature finds it more economical — to get into figurative language — or easier to break down almost wholly the larval body — after a new food-supply for further develop¬ ment has been got and stored away, and to build up from primitive undifferentiated cell begin¬ nings the final definitive butterfly body, than to make over these very unlike larval parts into the adult ones. The pupal stage, quiescent, non-food taking, and defended by a thick chitinous wall, often enclosed in a silken cocoon, buried in the ground or crevice, or harmonizing so perfectly with its environment as to be indistinguishable from it, is the chief period of this radical and marvelous breaking down and building anew. It is an inter¬ polated stage in the development of the butterfly corresponding to nothing in the phyletic history ; an adaptation to meet the necessities of its life- conditions. To my mind, this is the interpretation of the phenomena of complete metamorphosis.

Fig. 85. — Cross-section of newly developing muscle in pupa of honey-bee, Apis mel- lifica. (Greatly mag¬ nified.)

CHAPTER III

THE CLASSIFICATION OF INSECTS

As has been explained in the preceding chapter, insects are primarily classi¬ fied on the basis of their postembryonic development. Insects with incom¬ plete metamorphosis, that is, those which do not undergo a non-feeding, usually quiescent, pupal stage in their development are believed to be more nearly related to each other than to any of the insects which undergo a so- called complete metamorphosis. So they are spoken of collectively as the Hemimetabola, while all the insects with a distinct pupal stage are called the Holometabola. But when one has collected an adult insect, as a fly or moth or grasshopper, and wishes to classify it, this primary classification based on character of development often cannot be made for lack of informa¬ tion regarding the life-history of the particular insect in hand. The next grouping is into orders, and this grouping is based chiefly on structural characters, and corresponds to one’s already more or less familiar knowledge of insect classification. Thus all the beetles with their horny fore wings constitute one order, the Coleoptera; the moths and butterflies with their scale-covered wings another order, the Lepidoptera; the two-winged flies the order Diptera, the ants, bees, wasps, and four-winged parasitic flies the order Hymenoptera, and so on. So that the first step in a beginner’s attempt to classify his collected insects is to refer them to their proper orders.

Now while entomologists are mostly agreed with regard to the make-up of the larger and best represented orders, that is, those orders containing the more abundant and familiar insects, there are certain usually small, obscure, strangely formed and more or less imperfectly known insects with regard to whose ordinal classification the agreement is not so uniform. While some entomologists incline to look on them simply as modified and aberrant members of the various large and familiar orders, others prefer to indicate the structural differences and the classific importance of these differences by establishing new orders for each of these small aberrant groups. Most entomologists of the present incline toward this latter position, so that whereas Linnaeus, the first great classifier of animals, divided all insects into but seven orders, the principal modern American * text-book of systematic entp-

* Comstock, J. H., A Manual of Insects, 1898.

52

The Classification of Insects

53

mology recognizes nineteen distinct ones. This does not mean, of course, that twelve new orders of insects have been found since Linnaeus’s time, although two or three of the orders are in fact founded on insects unknown to him, but means that certain small groups classified by Linnaeus simply as families in his large orders have been given the rank of distinct orders by modern systematists. And as our knowledge of insects and their relationship to each other is certainly much larger now than it was one hundred and fifty years ago, we may feel confident that the many-order system of classifica¬ tion is more nearly a true expression of the natural interrelationships of insects than was the old seven-order system. But not all entomologists agree on the nineteen-order system. Few, indeed, still use the Linnsean system, but many believe that the division of the insect class into nineteen orders gives too much importance to certain very small groups and to some others which are not markedly aberrant, and these entomologists recognize a lesser number of orders, varying with different authors from nine to about a dozen. In this book we shall adopt the nineteen-order system as used in Comstock’s Manual. In the first place the author believes that this classi¬ fication best represents our present knowledge of insect taxonomy; in the second place this is the classification taught by nearly all the teachers of entomology in America.

To determine the order to which an insect belongs we make use of a classifying table or key. In the Key to Orders which follows this para¬ graph, all the insect orders are characterized by means of brief statements of structural features more or less readily recognized by simple inspection of the superficies of the body; to determine some of the conditions a simple lens or hand-magnifier will be needed. The orders are so arranged in the key that by choosing among two or more contrasting statements the student may “trace” his specimen to its proper order. Inspection of the Key with an attempt or two at tracing some familiar insect, as a house-fly, moth, or wasp whose order is already known, will make the method of use apparent. It must be borne in mind that young insects, such as caterpillars of moths, grubs of beetles, and the wingless nymphs of locusts, dragon-flies, etc., cannot be classified by this key. Indeed the young stages of most of the insects which we know well as adults are unknown to us, and there is, besides, such manifold adaptive variety in the external structure of those forms which we do know that no key for the classification into orders of immature insects can now be made.

54

The Classification of Insects

KEY TO THE ORDERS OF INSECTS.

(Arranged by Prof. H. E. Summers.)

(For adult insects only. If in any paragraph all the italicized characters agree with the specimen in hand, the remaining characters need not be read; these latter are for use in doubtful cases, or where the organs characterized in italics are rudimentary or absent. The technical terms used in this Key have all been defined in Chapter I.)

A. Primitive wingless insects; month-parts well developed, but all except the apices o} the mandibles and maxillce withdrawn into a cavity in the head; tarsi (feet) always one- or two-clawed; body sometimes centiped-like, with well-developed abdominal legs,

in this case tarsi two-clawed . (The simplest insects.) Aptera.

AA. Normally winged insects, wings sometimes rudimentary or, absent; mouth-parts not withdrawn into a cavity in the head.

B. Mouth-parts, when developed, with both mandibles and maxillce fitted for biting; abdomen broadly joined to thorax; tarsi never bladder -shaped; when mouth- parts are rudimentary, if the wings are two, there are no halteres (p. 303) ; if the wings are four or absent, the body is not densely clothed with scales.

C. Posterior end of abdomen with a pair of prominent unjointed forceps-like appendages; fore wings, when present , short, veinless, horny or leathery.

(Earwigs.) Euplexoptera. CC. Posterior end of abdomen usually without prominent unjointed forceps-like appendages; when- these are present the fore wings are always developed, veined.

D. Fore wings, when present, veined and membranous, parchmer^t-like or leathery; when absent, the labium (under-lip) either cleft in the middle, or the mouth-parts prolonged into a distinct beak.

E. Fore wings, when present, thicker than hind wings, somewhat leathery or parchment-like ; hind wings folded several times lengthwise, like a fan, in repose; when wings are absent, pro¬ thorax large.

(Locusts, crickets, cockroaches, etc.) Orthoptera. EE. Fore wings membranous, of same structure as hind wings; hind wings usually not folded, but occasionally folded like a fan; when wings are absent, prothorax small.

F. Antennce inconspicuous.

G. Hind wings smaller than fore or absent; posterior end of abdomen with two or three many -jointed filaments.

(May-flies.) Ephemerida. GG. Hind wings not smaller than fore; posterior end of abdomen without many-jointed filaments.

(Dragon-flies and damsel-flies.) Odonata. FF. Antennce conspicuous.

G. Tarsi less than five-jointed; labium cleft in the middle.

H. Wings always present, although sometimes very small; hind wings broader than fore wings , folded in repose; prothorax large, nearly flat on dorsal surface.

(Stone-flies.) Plecoptera.

The Classification of Insects

55

HH. Hind wings, when present, not broader than fore wings, not jolded in repose ; prothorax small } collar-like.

I. Tarsi jour -jointed; wings, when present ,

equal in size . (Termites.) Isoptera.

II. Tarsi one- to three-jointed.

J. Tarsi one- or two-jointed; always wingless.

(Biting bird-lice.) Mallophaga. JJ. Tarsi usually three-jointed; occasionally two-jointed, in which case wings always present, fore wings larger than hind wings. (Book-lice, etc.) Corrodentia. GG. Tarsi jive-jointed, but with one joint sometimes dijjicult to distinguish; labium usually entire in middle, sometimes slightly emarginate.

H. Wings, when present, naked or slightly hairy; hind wings with or without jolded anal space; in jormer case prothorax large and nearly plat on dorsal surjace; in wingless jorms mouth prolonged into a distinct beak.

I. Mouth-parts not prolonged into a distinct beak, at most slightly conical.

(Dobsons, ant-lions, etc.) Neuroptera.

II. Mouth-parts prolonged into a distinct beak.

(Scorpion-flies, etc.) Mecoptera. HH. Wings, when present, thickly covered with hairs; hind wings usually with jolded anal space; pro¬ thorax small, collar-like; mouth not prolonged into a beak. (Caddis-flies.) Trichoptera. DD. Fore wings, when present, veinless; horny or leathery; when absent, labium entire, and mouth-parts not prolonged into a distinct beak.

(Beetles.) Coleoptera.

BB. Mouth-parts, when developed, more or less pitted jor sucking; sometimes also pitted in part (the mandibles) jor biting: in this case either (i) base oj abdomen usually strongly constricted , joined to thorax by a narrow peduncle, or (2) the tarsi bladder-shaped, without claws; when mouth is rudimentary either the wings are two and halteres are present, or the wings are four or none and the body (and wings if present) are densely clothed with scales.

C. Prothorax jree; body ( and wings ij present) never densely clothed with scales; maxillary palpi usually absent; when present, tarsi bladder¬ shaped, without claws.

D. Tarsi bladder-shaped, without claws; wings jour ( sometimes absent ), narrow, jringed with long hairs; maxillae triangular, with palpi.

(Thrips.) Thysanoptera. DD, Tarsi not bladder-shaped, usually clawed; wings not jringed with long hairs; maxilla ( when mouth is developed ) bristle-like, without palpi. (Bugs.) Hemiptera.

CC. Prothorax not jree; maxillary palpi present, sometimes rudimentary and difficult to see, in which case body (and wings if present) densely clothed with scales; tarsi never bladder-shaped, usually clawed.

56

The Classification of Insects

D. Mandibles ojten rudimentary , when present bristle-like.

E. Wings four ( sometimes wanting ), clothed with scales; body covered thickly with scales or hairs; mouthy when developed, a slender sucking proboscis, closely coiled under head.

(Moths and butterflies.) Lepidoptera. EE. Wings two {or wanting), naked or with scattered hairs; hind wings in winged forms represented by halteres; body either naked or with scattering hairs; mouth a soft or horny beak, not coiled under head.

F. Prothorax poorly developed, scarcely visible from dorsal

side . ; . (Flies.) Diptera.

FF. Prothorax well developed, distinctly visible from dorsal side; wings never present . (Fleas.) Siphonaptera.

DD. Mandibles well developed, fitted for biting; wings four {sometimes two or none), naked or with scattered hairs.

(Ichneumon-flies, gall-flies, wasps, bees, and ants.) Hymenoptera.

After one has classified an insect in its proper order there remains, first, the determination of the family (each order being composed of from one to many families), then of the genus (each family comprising one to many genera), and finally of the particular species of the genus (each genus includ¬ ing one to many species). This ultimate classification to species, however, will be possible to the amateur in comparatively few cases. There are so many species of insects (about 300,000 are known) that it would require many shelves of books to contain the descriptions of them all. As a matter of fact, in only a few orders have the descriptions of the species been brought together in manuals available for general students. For the most part the descriptions are scattered in scientific journals printed in various languages and wholly inaccessible to the amateur. There are less than 1000 different species of birds in North America; there are more than 10,000 known species of beetles. Now when one recalls the size of the systematic man¬ uals of North American birds, and realizes that ten such volumes would include only the insects of one order, it is apparent that complete manuals of North American insects are out of the question. Except in the case of the most familiar, wide-spread, and readily recognizable insect species we must content ourselves with learning the genus, or the family, or with the more obscure, slightly marked* and difficult members of certain large groups, as the beetles and moths, simply the order of our insect specimens.

When one has determined the order of an insect by means of the above key he should turn to the account of this particular order in the book (see index for page) and find the keys and aids to the further classification of the specimen which the author has thought could be used by the general student. Comparison with the figures and brief descriptions of particular species which are given in each order may enable the amateur to identify the exact species of some of his specimens. But the specific determination

The Classification of Insects

57

of most of the insects in an amateur’s cabinet (or in a professional ento¬ mologist’s either, for that matter) will have to be done by systematic specialists in the various insect groups. Few professional entomologists undertake to classify their specimens to species in more than the one or two orders which they make their special study. Duplicate specimens should be given numbers corresponding to those on specimens kept in the cabinet, and be sent to specialists for naming. Such specialists, whose names can be learned from any professional entomologist, have the privilege of retain¬ ing for their own collections any of the specimens sent them.

CHAPTER IV

THE SIMPLEST INSECTS (Order Aptera)

ERTAIN household pests which are not moths and do not look like fish, but which are com monly called “ fish-moths” (Fig. 86), are

our most familiar repre sentatives of the order of “ simplest in¬ sects. ’’ The “fish” part of the name comes from the

covering of minute scales which gives the body a silvery appearance, and the “moth” part is derived from our habit of calling most household insect pests “moths.”

Thus we speak of “buffalo-moths” when we refer to the carpet-feeding hairy larvae of certain beetles. When we say clothes-moths we are really using the word moth accurately, for in their adult condition these pests are true moths, although the injury to clothing is wholly done by the moth in its young or caterpillar stage.

Besides the fish-moths other not unfamiliar Aptera are the tiny “ springtails ” (Fig. 87), which sometimes occur in large numbers on the surface of pools of water or on snow in the spring. Others may be easily found in damp decaying vegetable matter, as discarded straw or old toadstools. They are provided with an odd little spring on the under side of the body by means of which they can leap from a few inches to a foot or more into the air. Hence their common name.

In the order Aptera are included the simplest of living insects. By “simplest” is meant most primi¬ tive, most nearly related to the ancestors of the whole insect class. Also, as might be expected, these most primitive insects are simplest in point of bodily struc¬ ture; but in this respect they are nearly approached by simple-bodied members of several other orders.

These latter forms, however, have a simple body- structure due to the degradation or degeneration of a more complex type.

58

Fig. 86. — The fish- moth, Lepisma saccharina. (After Howard and Mar- latt; twice natural size.)

Fig. 87. — The pond-sur¬ face springtail, Smyn- thurus aquations. (After Schott; much enlarged.)

The Simplest Insects

59

It is familiar knowledge that animals which live parasitically on others, or which adopt a very sedentary life, show a marked degeneration of body structure, an acquired simplicity due to the loss of certain parts, such as organs of locomotion (wings, legs), and of orientation (eyes, ears, feelers, etc.). Thus the parasitic biting bird-lice (order Mal- lophaga, see p. 113), which live their whole lives through on the bodies of birds, feeding on the feathers, are all wingless and of gener¬ ally simple superficial structure. They are nearly as simple externally perhaps as the Aptera, but we believe that they are the degenerate descendants of winged and in other ways more complexly formed ancestors.

Similarly certain species of insects in

nearly all orders have adopted a life-habit Flshowin^theagsregmental: dfspo’S which renders flight unnecessary, and these tion of the ovarial tubes in three

insects having lost their wings are in this ^fsZ,gc"camfodeaPy(klter character simpler than the winged kinds. Targioni-Tozzetti; much en- Examples of such insects are the worker larged.)

ants and worker termites, many household insects, as the bedbugs and fleas,

and many ground-haunting forms, as some of the crickets, cockroaches, and beetles.

The Aptera, however, owe their sim¬ plicity to genuine primitiveness; among all living insects they are the nearest repre¬ sentatives of the insectean ancestors. But not all the Aptera are “simplest.” That is, within the limits of this small order a considerable complexity or specialization of structure is attained, although all the Aptera are primitively wingless, as the name of the order indicates.

These insects develop “without meta¬ morphosis”; that is, the young (Figs. 90 and 94) are almost exactly like the parents Fig. 89.— Diagrammatic figures Show- except in size. They have simply to grow ing the respiratory system in three larger and to become mature. In internal

Nicoletial C, Japyx. (After Tar- structure the simpler Aptera show some gioni-Tozzetti; much enlarged.) most interesting conditions. Their internal systems of organs have a segmental character corresponding to the external segmentation of the body. The ovarial tubes, which are gathered into

6o

The Simplest Insects

two groups or masses, one on each side of the body, in all other insects (Fig. 66), are separate and arranged segmentally in Japyx (Fig. 88), and less markedly so in Machilis; the respiratory system of Machilis (Fig. 89) consists of nine pairs of distinct, segmentally arranged groups of tracheae (air- tubes), while the ventral nerve-cord has a ganglion in almost every seg¬ ment of the body. As insects are certainly descended from ancestors whose bodies were composed of segments much less interdependent and coordi¬ nated than those of the average living insect, those present-day insects which have the body both externally and internally most strongly segmented are believed to be the most generalized or primitive of living forms. In addi¬ tion to the segmented character of the internal organs we have also another strong evidence of the primitiveness of the order in the possession by several Aptera of rudimentary but distinct external pairs of appendages on the abdominal segments, appendages undoubtedly homologous with the thoracic legs, and probably well developed in the insect ancestors as abdominal legs like those of the centipeds.

The order Aptera is composed of two suborders, which may be dis¬ tinguished as follows:

Abdomen -elongate, composed of ten segments, and bearing long bristle-like or shorter forceps-like appendages at its tip; no sucker on ventral side of first ' abdominal segment; antennae many-segmented . Thysanura.

Abdomen short and robust, composed of six segments, and usually with a forked spring at tip (usually folded underneath the body), and with a ventral sucker on first abdominal segment; antennae 4- to 8-segmented . Collembola.

Thysanura. — This suborder includes three families (a problematical

fourth family is found in Europe), as follows:

Body covered with scales . Lepismid^e

Body not covered with scales.

Tip of abdomen with forceps-like appendages . Japygid^e.

Tip of abdomen with slender many-segmented appendages . Campodeid^e.

To the last family in the above key belongs the interesting creature Campodea stapliylinus (Fig. 90), which zoologists regard as the most primi¬ tive living insect. It is small, white, flattened, wingless, and so soft-bodied and delicate that it can hardly be picked up uninjured with the most deli¬ cate forceps. It is about \ inch long (exclusive of caudal appendages), and is to be looked for under stones and bits of wood. I have found it in Ger¬ many, in New York, and in California, which indicates its wide distribu¬ tion. Other collectors have taken it in Italy, England, and in the Pyrenees. It is said to live also in East India. Is it not a little surprising that this most primitive, wholly defenceless, and ancient insect should be able to live successfully the world over in the face of, and presumably in competition with, thousands of highly developed specialized modern insect forms? It

The Simplest Insects

61

is a striking proof that Nature does not inevitably crush out all of her first trials in favor of her later results!

The Campodeidae contain another genus, Nicoletia (Fig. 91), one species of which, N. texensis , has been found in Cali¬ fornia and Texas, and which may be dis¬ tinguished from Campodea by its posses- d sion of three caudal appendages instead of two as in the latter form.

The Japygidae include but a single genus, Japyx, represented in this country by two described species and several as yet undescribed forms found at Stanford Uni¬ versity. Japyx subterraneus is a species first found under stones at the mouth of a small grotto near the Mammoth Cave

(Kentucky). Japyx (Fig. 92) is larger Fig. 90.— Young and adult of Ca

podea staphylinus (from California), the simplest living insect. (Natural size indicated by line.)

than Campodea, being about one-half inch long, and is readily recognized by its caudal forceps. Like Campodea its body is white and soft.

The Lepismidse include the familiar household fish- moths and a number of similar forms which live under stones and logs in soft soil at the bases of tree-trunks, under dead leaves in woods, and sometimes on the damp sand of seashores. Three genera of this family occur in North America, which may be distinguished as follows:

Caudal appendages short; prothorax very wide and body

behind it tapering rapidly . Lepismina.

Caudal appendages long; body elongate and tapering gradually backward.

Eyes large and close together . Machilis.

Eyes small and far apart . Lepisma.

Lepisma is best known by the species L. saccharina

(Fig. 86), which is the silverfish or fish-moth of the

house. It is silvery white, with a yellowish tinge on

the antennae and legs, and is from one-third to two-

fifths of an inch long. The three long caudal appen-

ensis , from Califor- dages, characteristic of the genus, are conspicuous. It

nia. (Eight times nat- feecjs chiefly on sweet or starchy materials, sometimes ural size.) _ . ; . ...... . .

doing much damage m libraries, where it attacks the

bindings. It attacks starched clothing, eats the paste off the wall-paper,

62

The Simplest Insects

causing it to loosen, and infests dry starchy foods. It runs swiftly and avoids the light. It can be fought by sprinkling fresh pyrethrum powder in bookcases, wardrobes, and pantries. Another species, L. domestica (Fig. 93), called the bake-house silverfish, is often common about fireplaces and ovens, running over the hot metal and bricks with surprising immunity from the effects of the heat. This habit has gained for it in England, according to Marlatt, the name of “fire- brat.” It can be distinguished from the species saccharina by the presence of dark markings on the Fig. 92. — Japyx sp., from back. Both saccharina and domestica are common natura^size /FlVe times in England, and saccharina probably came to this country from there.

Machilis (Fig. 95) does not occur in houses, but is more common than Lepisma outdoors. It is to be found under stones, in the soil around the base of tree-trunks, among dead leaves and fallen pine-needles, and at least one species occurs in the sand of sea-beaches.

Fig. 93. Fig. 94.

Fig. 93. — The fish-moth, Lepisma domestica. (After Howard and Marlatt; a little larger than natural size.) /

Fig. 94. — Young and adult of Lepisma sp., from California. (Twice natural size.)

Collembola. — The springtails, mostly of microscopic size, and wholly unfamiliar to any but persistent explorers of nature, comprise many more species than the Thysanura. Their most distinctive character is the pos¬ session, by most of them, of the forked spring (Figs. 96 and 97), by means of which they leap vigorously when disturbed. This spring is

The Simplest Insects

63

attached to the next to last body segment or to the antepenultimate one. It consists of a basal part and of two terminal processes.

It is carried bent forward under the body, with the bipartite tip held in a little catch on the third abdominal segment.

In some species the catch is lacking. The springtails also possess a curious organ on the ventral aspect of the first abdominal segment which appears to be a small projecting sucker or tube. This sucker is often more or less divided into two parts, in one family consisting plainly of two elongate, delicate tubes (Figs. 96 and 97). The use of this peculiar structure has not been definitely determined.

Some entomologists think that it serves as a clinging organ, enabling the insect to attach its body firmly to the object upon which it rests. Others believe that the sucker serves in some way to take up moisture, while still others be¬ lieve it to aid in respiration. The Collembola as well as the Thysanura cannot live in a dry atmosphere.

This suborder is divided into five families, as follows {MacGillivray) :

A. Spring wanting . Aphorurid^e.

lis sp., from Cali-

B. Spring arising from ventral side of fornia. (Three

antepenultimate abdominal segment. times natural

PoDURimE. size.)

BB. Spring arising from ventral side of penultimate abdom¬ inal segment.

C. Abdomen elongate, cylindrical, much longer than

broad . Entomobryid.e.

CC. Abdomen globular, but little larger than broad.

D. Terminal segment of antennse long, ringed.

Smynthurid^e.

DD. Terminal segment of the antennae short, with a whorl of hairs . Papiriid^e.

Of these five families the members of one, the Aphoruridae, in which the spring is wanting, are non-saltatorial. In all of the others leaping is a characteristic habit. The Smynthuridae and the Papiriidas are represented by but one genus each, viz., Smynthurus and Papirius.

Smynthurus hortensis is a common form in gardens, and may be called the “garden-flea.” It is found in the Eastern States in May and June “upon the Fig. 97. — The spotted

leaves of young cabbage, turnip, cucumber, and fpringta.il, Papirius macu~ J ° 0 r ’ losus, with spring extended,

various other plants, and also on the ground. It (Natural length, 2 mm.)

AA. Spring present.

Fig. 96. — The spotted springtail, Papirius maculosus, with spring folded underneath body. (N a t u r a 1 length, 2 mm.)

64

The Simplest Insects

is dull black, with head, legs, and bases of the antennae rust-color.” Smyn- thurus aguaticus (Fig. 87) often occurs in great numbers on the surface of pools. The insects look like tiny black spots on the water surface, but a

little observation soon reveals their lively character.

The Poduridae and Entomobryidae are represented in North America by twelve and fourteen genera respeC' tively. • Many of the Podurids are covered with scales and are often prettily colored and patterned. The scales (Fig. 98) are very minute and bear many fine lines and cross-lines, regularly arranged. On this account Fig. 98. Fig. 99. they are much used as test objects

^'IMurra7SCgreatfy°magnifiednf*a^' for microscopes, the quality of the

Fig. 99.— The snow-flea, Achorutes nivicola. lens being determined by its capacity (After Folsom; much enlarged.) to reveal their extremely fine mark¬

ings. One of the most interesting Podurids is the snow-flea, Achorutes nivicola (Fig. 99),. which gathers in large numbers on the surface of snow in the late spring. Comstock says that the snow-flea is sometimes a pest where maple- sugar is made, the insects collecting in large quantities in the sap.

An interesting representative of the Entomo¬ bryidae is the house springtail, Lepidocyrtus ameri- canus (Fig. 100), said by Marlatt to be “not infrequently found in dwellings in Washington.”

It is about one-tenth of an inch long, silvery gray, with purple or violet markings. In Europe also one species of springtail is common in houses. As these insects live on decaying vege¬ table matter, they probably do no special harm in the house. They especially frequent rather moist places, and may often be found in window-plant boxes and conservatories.

Fig. ioo. — The American springtail, Lepidocyrtus americanus , ventral aspect, showing spring folded un¬ derneath body. (After Howard and Marlatt ; much enlarged.)

CHAPTER V

THE MAY-FLIES (Order Ephemerida) and STONE- FLIES (Order Plecoptera)

AY-FLIES, lake-flies, or shad-flies, common names for the insects of the order Ephemerida, are familiar to

people who live on the shores of lakes or large rivers,

but are among the unknown insects to most high-and-

dry dwellers.

Travelling down the St. Lawrence River from Lake Ontario to Quebec one summer, I had hosts of day-long companions in little May-flies that clung to my clothing or walked totteringly across my open book. The summer residents of the Thousand Islands get tired of this too-constant com¬ panionship, and look resentfully on the feeble shad-fly as an insect pest. One evening in August, 1897, my attention, with that of other strollers along the shore promenade at Lucerne, was called to a dense, whirling, tossing haze about a large arc light suspended in front of the great Schweizerhof.

Scores of thousands of May-flies, just issued from the still lake, were in

violent circling flight about the blinding light, while other thousands were steadily dropping, dying or dead, from the dancing swarm to the ground. Similar sights are familiar in summer-time in this country about the lights of bridges, or lake piers and shore roads. This flying dance is the most conspicuous event in the life of the fully developed, winged May-fly, and indeed makes up nearly all of it. With most species of May-flies the winged adult lives but a few hours. In the early twilight the young May-fly floats from the bottom of the lake to the surface, or crawls up on the bank, the skin splits, the fly comes forth full-fledged, joins its thousands of issuing companions, whirls and dances, mates, drops its masses of Vggs on to the the lake’s surface, and soon flutters and falls after the eggs. It takes no food, and dies without seeing a sunrise. Sometimes the winds carry dense clouds of May-flies inland, and their bodies are scattered through the streets of lakeside villages, or in the fields and woods. Sometimes the great swarms

65

66

The May-flies and Stone-flies

fall to

the water’s surface and there are swept along by wind and wave, until finally cast up in thick winrows, miles long, on the lake beach. Millions of dead May-flies are thus piled up on the shores of the Great Lakes.

We call the May-flies the Ephemerida, after the Ephemerides of Grecian mythology, and the name truly expresses their brief existence — above water. But they have lived for a year at least before this, or for two or even three^y^ars, as wingless, aquatic creatures, clinging concealed to the under side of stones in the lake or stream bottom, or actively crawling about after their food, which consists of minute aquatic plants and animals or bits of dead organic matter. In this stage their whole environment, habits, and general appearance are radically different from those of the brief adult life. We can only guess, if our curiosity compels us to attempt some explanation, at the manner and the cause of such a strange life-history. What advantage is there in such a specialized condition that Nature could not have arrived at by less indirect means ? What is indeed the utility of the whole modification? The quick answer “utility,” which is to account for all such strange structural and physiological conditions on the basis of useful adapta¬ tions brought about by the slow but persistent action of natural selection, leaves us, confessedly, answered simply on a basis of belief. In hundreds of cases that may come under our observation, in how few are we really able to perceive a reason-satisfying course of adap¬ tive development based on the selection of useful small fluctuating variations ?

The eggs of the May-fly fall from the body of the mother to the water’s surface in two packets, which, Jj however, break up while sinking, so that the released

Fig. ioi. — May-flies about an electric lamp.

6/

The May-flies and Stone-flies

eggs reach the bottom separately. From each egg hatches soon a tiny flattened, soft-bodied, six-legged creature called a nymph, without wings or wing-pads, and looking very much like a Campodea (the simplest living insect, see p. 61). This nymph crawls about, feeds, grows, moults, grows, moults again and again (in a species observed by Lubbock there were twenty-one moultings), and finally at the end of . a year, or of two or three years, depending on the species, is ready to issue as a winged adult. During the nymphal life wings have been slowly developing, visible as short pads projecting from the dorsal margins of the meso- and meta-thorax, and appearing visibly larger after each moulting (Fig. 102). Respiration is accomplished by flat, leaf-like gills (Fig. 102) (these do not appear in some species until after one or two moultings), arranged segmentally along the sides of the abdomen. The mouth-parts are well developed for biting and chewing, with sharp-pointed jaws (mandibles). During its aquatic life at the bottom of stream or pond the May¬ fly has to undergo all the vicissitudes of an exposed and protracted life; it is eagerly sought after by larger, fierce, predaceous insects, stronger of jaw and swifter than itself; it is the prized food of many kinds of fishes, and it has to struggle with its own kind for food and place.

At the end of the immature life the nymphs rise to the surface, and after floating there a short time suddenly split open the cuticle along the back and after hardly a second’s pause expand the delicate wings and fly away. Some nymphs brought into the laboratory from a watering-trough at Stanford University emerged one after another from the aquarium with amazing quickness. Almost all other insects require some little time after the final moulting for the gradual unfolding of the wings, and dry¬ ing and strengthening of the body-wall, before flight or other locomotion. Most of the May¬ fly species go through another moulting after acquiring wings, a phenomenon not known to occur in the case of any other insect. The stage between the first issuance from the water with expanded wings and the final moulting is called the subimago stage, and may last, in various species, from but a few minutes to twenty-four hours. Such is, in general, the life-history of the May-flies. As a matter of fact, the life-history of no single May-fly species has yet been followed completely

Fig. 102. — Young (nymph) of May-fly, showing (g) tracheal gills. (After Jenkins and Kellogg; three times nat¬ ural size.)

68

The May-flies and Stone-flies

through. And here is an opportunity for some keen-eyed amateur ento¬ mologist to add needed facts to our knowledge of insect life.

The breathing-organs of the nymph are of interest, as special adaptations to enable them to take up oxygen and give off carbon dioxide without com¬ ing to the surface, as do the water-beetles, water-bugs, mosquito-wrigglers, and many other familiar aquatic insects. Each plate-like gill (Fig. 102) is a flattened sac, with upper and lower membranous walls which run into each other all around the free margin. Inside this sac is an air-tube

(tracheal trunk) with numer¬ ous fine branches. By osmosis an interchange of gases takes place through the walls of the tracheae and of the sac — car¬ bonic dioxide passing out, and air from that held in solution in the water passing in. If a nymph held in a watch-glass of water be watched, at times all the gills will be seen rap¬ idly vibrating, thus setting up currents and bringing fresh aerated water to bathe the gills.

In the adult winged stage (Fig. 103) the May-flies are extremely frail and delicate¬ bodied. The wings are fine and gauzy, consisting of the thinnest of membranes stretched over a perfect net- Fig. 103. — May-flv, from California. (Natural size.) WOrk of veins. The fore

wings are always markedly larger than the hind wings; in some species the latter are very small indeed, or even wanting altogether (Fig. 104). The body-wall is weakly chitinized, and collected specimens almost always shrivel and collapse badly in drying. The abdomen usually bears two or three long filaments on its tip; the head is provided with compound eyes and short awl-like antennae. The often-repeated statement in text-books that adult May-flies have no mouth nor mouth-parts is not literally true of all species, as weakly developed jaws and lips are present in some. But they are in such weak and atrophied condition that they can hardly be func¬ tional. It is probable, therefore, that no adult May-fly takes food. In the males of some species the compound eyes present a very interesting

The May-flies and Stone-flies

69

condition, being divided, each into two parts, by a narrow impressed line or by a broader space (Fig. 105). The two parts differ in the size of the facets of the ommatidia, i.e., eye-elements, and it has been ascertained (Zim¬ merman, 1897) that this difference in size of facets is accompanied by other and more important structural differences, which make it certain that the two parts of the eye have different powers of seeing. One part is especially adapted for seeing in the dark, or for detecting slight differences in intensity of light, but is ill-fitted for exact sight, while the other part is adapted for seeing in daylight, and for making a more exact picture of outline. As the mating flights occur usually at twilight or in the evening, Zimmerman believes that this modification of the eyes of the males is to enable them to discover the females in the whirling shadow-dances. Chun has recorded a similar division and difference in the eye of certain ocean crustaceans and believes that the

“dark eyes” are used for seeing in the dimly Fl(fi i°4' May"fly’. C(Bms , . , l T . . . ... . .... . dirmdiata, possessing only-

lighted water below the surface, while the light one pair of wings. (Much

eyes” are for special use at the brilliantly lighted enlarged.)

surface. I have noted similar conditions in the eyes of both male and

female net-winged midges (Blepharoceridae) , small, two-winged flies of

particularly interesting life (see p. 319). It is unusual to find such parallel

adaptations in forms so unrelated.

The May-flies show an anatomical condition of much interest to ento¬ mologists in the paired openings for the issuance of the eggs. Insects have their organs arranged in pairs, one on each side of the middle line of the body, as the legs, wings, mouth-parts, antennae, eyes, spiracles, etc., or exact¬ ly on the middle line, as the heart, alimentary canal, and ventral nerve- cord. That is, the typical insect body is bilaterally symmetrical, and the more apparent this symmetry is the sim¬ pler and more generalized the insect is believed to be. All other insects but the May-flies have the two egg- ducts, one from each egg-gland, fused inside the body, so as to form a short, single, common duct on the median line. But the May-flies have the ducts

Fig. 105. — Section through head of male May-fly, Potamanthus brunneus, showing composition of compound eye and two sizes of eye-elements (ommatidia). (After Zimmer; greatly magnified.)

7°

The May-flies and Stone-flies

separate; that is, paired and bilateral for their whole course. This is taken to be an indication of the primitiveness and antiquity of the order.

If the May-flies are an ancient group of insects, and there is little doubt of this, we have in them another example (we have previously noted one in the case of Campodea, see p. 60) of primitive insects of excessively frail and defenceless character persisting in the face of the strenuous struggle for existence and of the competition, in this struggle, of highly developed, specialized insect forms. Perhaps the solution of this problem in the case of the May-flies is to be found in their extreme prolificness and in the ephemeral character of their adult lives. It is only in the adult condition that May-flies are so ill-fitted to defend themselves; so they simply make no attempt to do so. They lay their eggs immediately on coming of age, and thus accomplish the purpose of their adult stage. In their immature form they are not so handicapped in the struggle for existence, although they seem by no means in position to compete with some of their neighbors, like the nymphs of the stone-fly and dragon-fly.

About 300 species of Ephemerida are known, of which 85 occur in North America. Their classification has been comparatively littlfe studied and is a difficult matter for beginners. The differences among the adults are so slight, and the preserved specimens are so uniformly misshapen and dried up, that most of us will have to be satisfied with knowing that we have in hand a May-fly, without being able to assign it to its genus. Keys to the North American tribes and genera of May-flies may be found by the student who may wish to attempt the generic determination of his specimens, in a paper by Banks in the Transactions of the American Ento¬ mological Society, v. 26, 1894, pp. 239-259.

There are better defined differences among the nymphs than among the adults, but unfortunately the nymphs have been as yet too little studied for the making out of a comprehensive key to the genera. Needham and Betten give an analytical table of genera of Ephemerid nymphs as far as known in the Eastern United States, in Bulletin 47 of the New York State Museum, 1901.

On the under side of the same stones in the brook “ riffles’ ’ where the May-fly nymphs may be found, one can almost certainly find the very similar nymphs (Fig. 106) of the stone-flies, an order of insects called Plecoptera. More flattened and usually darker, or tiger-striped with black and white, the stone-fly nymphs live side by side with the young May-flies. But they are only to be certainly distinguished from them by careful exam¬ ination. The gills of the immature stone-flies usually consist of single short filaments or tufts of short filaments rising from the thoracic segments, one tuft just behind each leg (Fig. to6), and not flat plates attached to the sides

The May-flies and Stone-flies

71

of the abdomen as in the May-fly nymphs. The feet of the stone-flies have two claws, while those of the young May-flies have but one. The stone-fly nymph has a pair of large compound eyes, as well as three small simple eyes, strong jaws for biting and chewing (perhaps for chewing heir nearest neighbors, the soft-bodied, smaller May-fly nymphs!), and two slender back¬ ward-projecting processes on the tip of the abdomen.

The legs are usually fringed with hairs, which makes them good swimming as well as running organs.

The nymphs can run swiftly, and quickly conceal themselves when disturbed.

All stone-fly nymphs, as far as known, require well aerated water; they cannot live in stagnant pools or foul streams. Needham says that a large number of the smaller species are wholly destitute of gills absorbing the air directly through the skin.

Nymphs brought in from a brook and placed in a Fl^ ^ £OU from^Cal? vessel of still water will be seen with claws affixed, fornia. (Twice natural vigorously swinging the body up and down, trying size.) to get a breath under the difficult conditions into which they have been brought. The food-habits are not at all well known: some entomologists assert that small May-fly nymphs and other soft-bodied aquatic creatures are eaten, while others say that the food consists of decaying organic matter.

Here is another opportunity for some exact observation by the interested amateur. On the other hand it is per¬ fectly certain that the nymphs themselves serve as food for fishes.

The fully worked-out life-history of no stone-fly seems to have been recorded. The eggs, of which 5000 or 6000 may be deposited by a single female, are probably dropped on the surface of the water, and sink to the bottom after being, however, well distributed by the swift current. Sometimes the eggs are carried about for a while by the female, enclosed in a capsule attached to the abdomen. The young moult several times in their growth, but

Fig 107 — Exuvia Probably not nearty as many times as is common among of nymph of stone- May-flies. When ready for the final moulting, the nymph fly. (Natural size.) crawis out 0n a rock or on a tree-root or trunk on the bank, and splitting its cuticle along the back, issues as a winged adult. The cast exuviae (Fig. 107) are common objects along swift brooks.

The adults (Fig. 108) vary much in size and color, the smallest being less than one-fifth of an inch long, while the largest reach a length of two

7 2

The May-flies and Stone-flies

inches. Some are pale green, some grayish, others brownish to black. There are four rather large membranous, many-veined wings without pattern, the hind wings being larger than the front ones. When at rest, the fore wings lie flat on the back, covering the much-folded hind wings. The mouth- parts are present and are fitted for biting, although the food-habits are not known. It is asserted that some species take no food. The antennae are long and slender. The abdomen usually bears a pair of long, many-seg- mented, terminal filaments. The body is rather broad and flattened, and there is no constriction between the thorax and abdomen. On the ventral aspect of each thoracic segment there is a pair of small openings whose func-

Fig. 108. — A stone-fly, Perla sp., common about brooks in California. (After Jenkins and Kellogg; twice natural size.)

tion is unknown. The adults of certain species retain, although in shriveled and probably functionless condition, the filamentous gills. This fact is of importance in connection with the question as to whether insects are descended from aquatic or terrestrial ancestors. Those who believe in the aquatic ancestry have found a simple origin for the spiracles (breathing- pores) by imagining them to be the openings left when the gills, used in aquatic life, were lost. But the adult stone-flies which retain their gills also have wholly independent spiracles.

About ioo species of stone-flies are known in North America. The adults are to be found flying over or near streams, though sometimes

The May-flies and Stone-flies

73

straying far away. They rest on trees and bushes along the banks. The green ones usually keep to the green foliage, while the dark ones perch on the trunk and branches. The various species are included in ten genera, which may be determined by the following table:

TABLE OF NORTH AMERICAN GENERA OF PLECOPTERA.

The following technical terms not heretofore defined are used in this key: cerci, slender processes projecting from the tip of the abdomen; radial sector , cubital vein, and other names of veins in the wings may be understood by reference to Fig. 109.

Fig. 109. — Diagram of venation of wing of a stone -fly; 1, costal vein; 2, subcostal vein; 3, radial vein; 4, medial vein; 5, first anal vein; 6, radial sector, P, pterostigma; A, arculus: av a2, az, apical cells. Between the medial and first anal vein is the cubital vein, not numbered. Cell M is the cell behind the medial yein; cell Sc is the cell behind the subcostal vein.

A. With two long, many-jointed cerci.

B. Radial sector not reduced, i.e., with four or more branches.

C. Wings strengthened throughout by many cross-veins, there being many cross-veins between the branches of the media, between the accessory cubital veins, and in the anal areas of both pairs of wings. .Pteronarcys. CC. Wings with few or no cross-veins between the branches of the media, between the branches of the cubital veins, and in the anal area.

D. Radial area of the fore wings with an irregular network of veins-

Dictyopteryx.

DD. Radial area of the fore wdng with no cross-veins except the radial

cross-veins, or with a few regular cross-veins - Perla (in part).

BB. Radial sector reduced, i.e., with less than four branches.

C. Hind wings much broader than the fore wings.

D. With several cross-veins in cell M of the fore wings.

E. Cell Sc of the fore wings with at least three cross-veins.

F. With three ocelli . Perla (in part).

FF. With only two ocelli. . . Pseudoperla.

EE. Cell Sc of the fore wings with only one or two cross-veins.

Small species of a green or yellow color . Chloroperla.

DD. With only one cross-vein in cell M of the fore wings between the

arculus and the medio-cubital cross-vein . Capnia.

CC. Hind wings of the same width as the fore wings; the anal area of the

hind wings not expanded . ‘. . . .Isopteryx.

AA. With the cerci rudimentary or wanting.

B. Second segment of the tarsi equal in length to the others; rudimentary cerci present . . T^eniopteryx.

74

The May-flies and Stone-flies

BB. Second segment of the tarsi small, shorter than the others, cerci absent.

C. Veins radiating from the ends of the radial cross-vein forming an X.

Nemoura.

CC. Veins radiating from the ends of the radial cross-vein not forming an X.

Leuctra.

The genus Perla (Fig. 108) includes more species than any other. The species of Pteronarcys retain gills in the adult condition. The species of Chloroperla are small, delicate, and pale green. Leuctra includes the slender¬ est of the stone-flies; they are small and brownish. Comstock says that there are several species of stone-flies that appear on the snow on warm days in late winter. They become more numerous in early spring, and often find their way into houses. The most common one in Central New York is the small snow-fly, Capnia pygmcea , which is grayish black. The female is 9 mm. (about § in.) long, with an expanse of wings of 16 mm. (about f in.), while the male is but 4\ mm. (about \ in.) long, and has short wings which extend but two-thirds the length of the abdomen.

CHAPTER VI

DRAGON-FLIES AND DAM¬ SEL-FLIES (Order Odonata)

HEN it is high noon on the mill-pond, — when leaves droop, and sun glares upon the water, and the air is hot and still, when other creatures seek the shade, and even the swallows that skim the air morning and evening are resting, — then those other swallows of the insect world, the dragon¬ flies, are all abroad. . . . One may stand by the side of a small pond, and follow for hours with his eye the evolutions of one of the large dragon-flies skim- .

ming over the surface in zigzag lines or sweeping curves, stopping still in midair, and starting again, seeming never to rest, nor even to tire. Poised

75

76

Dragon-flies and Damsel-flies

in the air, with the sunlight dancing on its trembling wings, it is indeed a beautiful sight.

“ ‘ Dragon-flies ? Folks call ’em devil’s-darnin’-needles in our parts, and they say they will sew up your ears.’ Yes; and in some localities they

M are called ‘snake-doctors,’ and are said to bring dead snakes to life ; and other meaningless names are given them, such as ‘snake-feeders,’ ‘horse-stingers,’ ‘mule- killers,’ etc.; but in spite of all these silly names and the silly superstitions they represent, dragon-flies are entirely harmless to man — are indeed to be counted as friends, for they destroy vast numbers of mosquitoes and gnats and pestiferous little flies. To such creatures they must seem real dragons of the air. While one is standing by the pond let him follow awhile the actions of a dragon¬ fly that is making short dashes in different Fig. Iio— A dragon-fly (from life), directions close to the bank. Let him

fix his eye on a little fly hovering in the air, and note that after the dragon-fly has made a dart toward it, it is gone. Let him repeat the observation as the dragon-fly goes darting hither and thither. It will be hard to see the flies captured, so quickly it is done, but one can see that ‘ the place that once knew them knows them no more.’ And the usefulness of the dragon-fly in taking off such water-haunting pests will be appreciated.”

Thus entertainingly and truthfully writes Professor Needham of the strong-winged, brilliantly colored, graceful insects of our present chapter. If one could see through muddy water and would fix his gaze on

the weed-choked slimy depths of the pond, Fig. hi. — The young (nymph) of

he would see the dragon-flies m another dragon %• (From Jenkins and ...... . .... Kellogg; twice natural size.)

stage of their life, under very different

conditions of existence, and in very different guise. Crawling awkwardly about over and through the decaying weeds and leaves and mud of the bottom or lying in ambush, half concealed by coverings of slime, would be seen certain strange big-headed, thick-bodied, dirty gray-green,

Dragon-flies and Damsel-flies

77

wingless creatures from half an inch to two inches long. Occasionally one of these creatures suddenly darts forward by spurting water from the hinder tip of its body; occasionally one quickly thrusts out from its head a vicious pincer-like organ which is more slowly withdrawn, or rather folded up, with an unfortunate tiny water-animal squirming in the toothed pincers. Still dragons, though now dragons of the deep instead of flying dragons, these are our insects in their immature or larval life. Their

Fig. 112. — Young (nymph) dragon-fly, showing lower lip folded and extended. (From Jenkins and Kellogg; twice natural size.)

prey, consisting of water-bugs, May-fly larvae, small crustaceans, mol- lusks, and any of the numerous aquatic insect larvae, including other young dragon-flies, is probably always caught alive. Not by active pursuit, as in the air above, but by lying in wait in the murky depths of the pond until the unsuspecting insect comes within reach of the extensible lower lip with its pair of broad spiny, jaw-like flaps at the clutching tip. The fierce face of the young dragon, with its great mouth and sharp jaws, is all concealed by this lip when folded up, and there is little in the appearance of the dirty, sprawling, smooth¬ faced creature to betray its dragon-like character. But appearances in the insect world may be as deceptive as in our own, and too late the careless water-bug out on a foraging swim for lesser prey finds himself in range of a masked battery and becomes the preyer preyed upon.

About three hundred different species of dragon- and damsel-flies (damsel-flies are the smaller, slender-bodied, narrow- winged kinds, see Fig. 1 13) are known in North America, about two thousand having been found in all the world. In any single locality where conditions are at all favor¬ able to dragon-fly life, that is, where there are live streams and ponds, from a score to two or three times as many different dragon-flies can be found. One hundred species occur in Ohio, and one hundred and twenty in New York, states offering specially favorable natural conditions for them, while only about fifty species have been found in California, a much larger but more arid region. The young of no dragon-fly species is known to live in salt water, although nymphs have been found in brackish water and in

78

Dragon-flies and Damsel-flies

streams impregnated with sulphur from sulphur springs. Nor do dragon¬ flies like cold weather. Although a few species are found in the far North (recorded at 70° N. in Norway, 65° N. in Alaska, and 63° N. in Siberia) and a few at high cold altitudes (as high as 10,000 feet) on mountain flanks, the great majority of them need considerable temperature for growth and development and even for activity during adult life. Calvert says that but one species is known which regularly passes the winter in adult stage, and

that most dragon-flies live as adults from but twenty-five to forty-five days, and * these in the summer. In California, where the winter temperature at sea-level only occasionally falls to 320 F., adult dragon¬ flies can be found in most of the months of the year.

The adult dragon-flies are to be seen pursuing their prey, like hawks, with swift darting flights over ponds, along streams, and even scattered widely inland over fields and in woods. A few kinds have a liking for the vicinity of houses. Needham, a careful student of these insects, has found that the hunting region above and along the shores of a pond may be imaginarily divided into zones one above the other, each zone characterized by the presence of a few particular dragon-fly species. “So, in fact,” he writes, “we find the smaller damsel- flies flying over the water in a straight course an inch or less above the surface, and rarely venturing higher; the larger damsel-flies a little higher; the amber wings at an average of about six inches; the larger skimmers a foot or more from the surface, and upland skimmers and darters still higher. One has only to stand a little while by some small area of water where all these are flying to see that each keeps rather closely to his proper altitude. Why do damsel-flies keep so close to water? The reason is not far to seek. Dragon-flies eat one another — the strong destroy the weak. If to venture up into the altitude of the larger species means to run the risk of being eaten, we can readily see why the damsel-flies should stay down below. The hawk may roam the air at will, but sparrows must keep to the bushes.”

We think of dragon-flies, as of albatrosses and Mother Carey’s chickens, as being always on the wing. They catch their prey while flying, eat it while flying, mate while flying, and some of them deposit their eggs while

Fig. 113. — Damsel-flies winged dragon-flies) . size; from life.)

(narrow-

(Natural

Dragon-flies and Damsel-flies

79

on the wing. But of course all dragon-flies rest sometimes, and some of them, especially the damsel-flies, are at rest most of the time, clinging to stems or leaves by the water’s edge. The larger kinds may be found occasionally perched on the tips of tall swaying reeds, or on a stump or projecting dead limb. From these coigns of vantage they swoop like a hawk on any rash midge that ventures awing in the neighborhood. Cold or cloudy weather, or a strong wind, will drive most dragon-flies to shelter.

The Odonata are unexcelled among insects for swiftness, straightness, and quick angular changes in direction of flight. The successful main¬ tenance of their predatory life depends upon this finely developed flight function together with certain structural and functional body conditions which might be said to be accessory or auxiliary to it. And this may be an appropriate place to describe briefly a few of their salient structural characteristics.

All dragon-flies have four well-developed wings, and all show such a similar general bodily make-up and appearance, that from an acquaintance¬ ship with two or three familiar species any member of the order can be recognized as really belonging to the group. The body in all is long, smooth, and subcylindrical or gently tapering. This clean, slender body offers little resistance to the air in flight, and serves as an effective steering-oar. The wings are long and comparatively narrow, fore and hind wings being much alike, almost exactly alike indeed in the damsel-flies. The venation is of the general type known as net-veining (Fig. 1146), the few strong longi¬ tudinal veins being connected by many short cross-veins. The fore wings are greatly strengthened along their costal (front) margin by having the first longitudinal (subcostal) vein behind the margin placed at the bottom of a groove, and the cross-veins in that groove so enlarged vertically as to take on the character of flat, plate-like braces or buttresses. As, in the figure-of-eight movement of the wing in flight, the front margin first meets the resistance of the air, it is necessary that swiftly and strongly beat¬ ing wings should be especially strengthened along this edge, and this is just what the peculiar folding and bracing of the costal region of the dragon-fly’s fore wing accomplishes.

The head is unusually large and is more than two-thirds composed of the pair of great compound eyes. More than 30,000 facets have been counted in the cornea of certain dragon-fly species, and this means that each eye is made up of more than 30,000 distinct eye-elements or ommatidia, each capable of seeing a small part or point of any object in range of vision. Thus an image of a near-by object is made in fine mosaic, and the finer the mosaic the more definite and precise is the vision by means of compound eyes. These great eyes, too, have facets directed up and down and sidewise

8o

Dragon-flies and Damsel-flies

as well as forward, and by a special sort of articulation of the head on the thorax it can be rotated readily through i8o°, so that the principal part of each eye can be directed sidewise or even straight down. For accurate flight and successful pursuit of flying prey the dragon-fly has full need of good eyes. It is to be noted, too, that the eyes are relatively largest in those particular dragon-fly kinds which have the most powerful flight. On the head, also, are three simple eyes (ocelli), the pair of very small awl-like antennse, and the great mouth. The mouth is overhung as by a curtain by the large flap-like upper lip (labrum). The jaws (mandibles) are strong and toothed, and obviously well adapted for tearing and crushing the cap¬ tured prey.

When the prey is come up with, however, it is caught not by the mouth but by the “ leg-basket.” The thorax is so modified, and the insertion of the legs such, that all the legs are brought close together and far forward, so that they can be clasped together like six slender, spiny grasping arms just below the head. Although the catching and eating is all done in the air and very quickly, observers have been able to see that the prey is caught in this ‘ £ leg-basket ” and then held in the fore legs while being bitten and devoured. These slender legs are used only very slightly for locomotion, but they serve well for the light unstable perching which is characteristic of the dragon-flies.

The internal anatomy is specially characterized, as might well be imagined, by a finely developed system of thoracic muscles for the rapid and powerful motion of the wings and the delicate and accurate move¬ ments of the legs. The respiratory system is also unusually well developed, such active insects needing a large quantity of oxygen, and generating a large amount of carbon dioxide. The respiratory movements, according to Calvert, consist in an alternate expansion (inspiration through the ten pairs of breathing-holes, or spiracles, arranged segmentally on thorax and abdomen) and contraction (expiration) of the abdomen. The rate of movement varies greatly at different times owing to unknown causes, but is always quickened by exercise, increased temperature, or mechanical irri¬ tation. In different dragon-flies the inspirations have been noted to be from 73 to 118 a minute.

The dragon-flies are famous for their beautiful metallic colors. As they dart through the air one gets glimpses of iridescent blue and green and cop¬ per, of tawny red and violet and purple reflections that are most fascinating and tantalizing. Seen close at hand in the collections, however, they are mostly dull-colored and, except for their “pictured” wings and the sym¬ metry and trim outline of their body, rather unattractive “specimens.” But a freshly caught dragon-fly shows the real glory of the coloring: delicate changing shades of green and violet and copper quiver in the great eyes;

Dragon-flies and Damsel-flies 8 i

the thorax is translucent green or blue, and the long symmetrical body is warm red or deep blue or purple or green. It is often covered with a soft whitish “ bloom,” that tones down the brilliant metallic iridescence. But as the body dries, the colors fade. They are due not so much to pigment as to the interference in reflection of the various color-rays, this interference being caused by the structure of the body-wall. Just as soap-bubbles or weathered plates of glass or mica produce brilliant colors by interference effects, so does the semi-transparent laminate outer body-wall of the dragon-fly produce its fleeting color glories. While the wings of many kinds are clear, unmarked by blotches or line, the wings of others bear a definite “picture” or pattern, usually light or dark brown or even blackish, reddish, thin yellow, or whitish. These wing-patterns make the determination of many of the dragon-fly species a very simple matter.

When the dragon-flies go winging about over ponds and streams they are engaged in one of three things: in eating, in mating, or in egg-laying. The prey of the dragon-fly may be almost any flying insect smaller than itself, although midges, mosquitoes, and larger flies constitute the majority of the victims. Howard says that the voracity of a dragon-fly may easily be tested by capturing one, holding it by its wings folded together over its back, and then feeding it on live house-flies. Beutenmiiller found that one of the large ones would eat forty house-flies inside of two hours. Howard says that a dragon-fly will eat its own body when offered to it (query, to its head ?) and that a collected dragon-fly, if insufficiently chloroformed and pinned, will when it revives cease all efforts to escape if fed with house-flies, the satisfying of its appetite making it apparently oblivious to the discom¬ fort or possible pain of a big pin through its thorax. That dragon-flies are sometimes cannibalistic has been repeatedly confirmed by observation. The nymphs have been seen to devour nymphs of their own and other species; the nymphs of a European form have been observed to come out of water at night and attack and devour newly transformed imagoes of the same species, while several instances are recorded of the capture and devouring of an imago of. one species by an imago of another.

The good that is done by dragon-flies through their insatiable appetite for mosquitoes is very great. Now that we recognize in mosquitoes not only irritating tormentors and destroyers of our peace of mind, but alarm¬ ingly dangerous disseminators of serious diseases (malaria, yellow fever, filariasis), any enemy of them must be called a friend of ours. A prize was once offered for the best suggestions looking toward practicable means of artificially utilizing dragon-flies for the destruction of mosquitoes and house¬ flies, but no very efficient improvement on the dragon-fly’s natural tastes and practices were brought out by this essay competition.

In Honolulu, the principal city of our mid-Pacific territory, the mosqui-

82

Dragon-flies and Damsel-flies

toes are so abundant that no one neglects to enclose his bed carefully each night in mosquito-netting, and all bedrooms are equipped with an ingenious canopy which can be folded closely in the daytime and readily spread over the bed at night. The continuous and abundant presence of mosquitoes is such a matter of fact that it has dictated certain particular habits of life to the inhabitants of Honolulu. But in the daytime one is singularly free from mosquito attack. Coincidentally with this one notes the surprising abundance and strangely domestic habits of great dragon-flies. I have watched dozens of dragon-flies hawking about a hotel lanai (porch) in the heart of the town. No pond or stream is nearer than the city’s outskirts. Dragon-flies are in the main streets, in all the gardens, and they are chiefly engaged in the laudable business of hunting the hordes of “day” mosquitoes to their death. The most conspicuous features of insect life in Hawaii are the hosts of dragon-flies by day and the hordes of mosquitoes by night. As the dragon-flies unfortunately are not night flyers (although some forms keep up the hunting until it is really dark), it is by night that one realizes what a plague the mosquito is in the islands. Were it not for the dragon¬ flies, life in the islands would be nearly intolerable. The rice- swamps and taro-marshes and the heavily irrigated banana and sugar plantations offer most favorable breeding-grounds for the mosquitoes, but also fortunately for the dragon-flies as well. The mosquitoes of Hawaii are not indigenous; they were introduced with white civilization. It is told, and is not improb¬ able, that the skipper of a trading schooner in early days, to revenge himself for some slight put on him by the natives, purposely put ashore a cask of water swarming with mosquito wrigglers. It needed no more than that to colonize this fascinating tropic land with the mosquito plague. How the saving dragon-flies came is not yet come to be tradition; indeed, few Hawaiians understand how important a part the dragon-fly plays in their life. They do appreciate the mosquito.

In the Samoan Islands, too, where we have another tropical colony, the mosquitoes are a great plague. Here the matter is made more serious. The Samoan mosquitoes are carriers and disseminators of a dreadful disease known as elephantiasis from the enormous enlargement of the legs and arms of sufferers from it. This disease is the great scourge of these islands, more than 30% (from my own observation; 40% and 50% are estimates given by other observers) of the natives having it. (For an account of the role of mosquitoes in the dissemination of malaria, yellow fever, and elephantiasis, see Chapter XVIII of this book.) The dragon-flies are, in Samoa as in 'Hawaii, conspicuous by their abundance and variety, and they do much to keep in check the quickly breeding mosquitoes.

Watching the flying dragon-flies over a pond, you may occasionally see one poising just over the surface of the water, and striking it with the

Dragon-flies and Damsel-flies 83

tip of the abdomen; or another kind may be seen to swoop swiftly down to the surface occasionally in its back-and-forth flight, and to dip the tip of

Fig. 1146.

Stages in the development of the giant dragon-fly, Anax junius. a, youngest stage; b, c , and d, older stages, showing gradual developme»t-o^£-lha- w-ings. (Young stage, slightly enlarged after Needham; adult three-fourths natural size.)

the body for a moment into the water. These are females engaged in laying their eggs. The eggs issue in small masses, usually held together by a gelat¬ inous substance. From several hundred to several thousand eggs are laid by

84

Dragon-flies and Damsel-flies

each female. Needham counted 110,000 eggs in a single egg-mass of Libellula. Sometimes the eggs may be laid on wet mud or attached to moist water- or shore-plants. The damsel-flies and a few of the dragon-flies insert the eggs in the stems of dead or living water-plants below the surface of the water. To do this they have to cling to the stem, with the abdomen or sometimes the whole body under water, and cut slits in it with the sharp ovipositor. The eggs are sometimes laid on submerged timbers and moss- or alga-covered stones. Kellicott observed females olLfl f^a^^^i^-4a-<lamsel-fly abundant along Lake Erie) to remain wholly under water for from five to fifty-five minutes at a time. These females were accompanied by males which also stayed under for similar lengths of time.

The eggs hatch after various periods, depending on the species of dragon¬ fly and on the time of year of oviposition. In midsummer Needham found the eggs of some species to hatch in from six to ten days, while others laid in autumn did not hatch until the following spring. In the same lot of eggs the period of incubation may vary even in midsum¬ mer from a week to more than a month.

From the eggs come tiny, spider-like nymphs with long, slender legs, thin body, and no sign of wings. Even in the largest dragon-fly species the just-hatched young are only about one-twelfth of an inch long, while the nymphs of the common Libellulas are only one-twenty-fifth of an inch long at hatching. They begin their predatory life, con¬ fining their attention at first to the smaller aquatic creatures, but with increasing size and strength and confidence being ready to attack almost any of the under-water dwellers. Even fish are seized by the larger nymphs, Needham having seen the nymphs of one species seize and devour young brook-trout as long as themselves.

The young of different species differ consider¬ ably in size, shape, and duration of their nymphal existence. The nymphs of some species require more than a year to develop into adults, while those of some others are ready to transform in a few months, not a few dragon-fly species having two gener¬ ations a year. The one-year life cycle, however, is usual among the more familiar dragon-flies, the eggs laid during midsummer hatching in late sum¬ mer, the nymphs hibernating and being ready to emerge the following sum¬ mer. Needham thinks that the damsel-flies have a number of broods in a season, the processes of transformation and oviposition beginning as soon

Fig. 115. — The young (nymph) of a damsel- fly (narrow-winged dra¬ gon-fly), Lestes sp. The three leaf-like processes at the tip of the abdo¬ men are gills (Twice natural size.)

Dragon-flies and Damsel-flies 85

as the weather permits, and continuing industriously to the close of the season.

The nymphs cast the skin repeatedly during their growth and develop¬ ment, although the exact number of moultings is not known for any species. After two or three moults the wing-pads appear and with each successive moult increase in size. Immediately after moulting the nymphs are light greenish or gray, and their characteristic color pattern is distinct, but they gradually darken, the pattern becoming more and more obscure until by the t’me for another moulting the body is uniformly dark and dingy. The nymphs (Fig. 115) of the damsel-flies are elongate and slender, and have three long conspicuous gill-plates at the tip of the abdomen, which they can also use as sculls for swimming. The dragon-fly nymphs are robust¬ bodied, some of them indeed having the abdomen nearly as wide as long and much flattened. All the nymphs are provided with the long grasping lower lip, which can be folded mask-like over the face when not engaged in seizing prey. The mandibles are strong and sharp and the whole mouth is well fitted for its deplorable but necessary business.

The true dragon-fly nymphs do not have plate-like gills, like those of the damsel-flies, nor any other external kind, but have the posterior third of the intestine lined with so-called internal gills. These internal or rectal gills are in six longitudinal bands, each consisting of two thin rows of small plates or tufts of short slender papillae. Water is taken into the intestine through its posterior opening and, after bathing the gills, giving up its dis¬ solved oxygen, and taking up carbon dioxide, it is ejected through the same opening. When this water is ejected violently it serves to propel the nymph forward. It is also apparently occasionally used for defence.

Just as the adult flying dragon-flies keep to certain regions above or in the neighborhood of the pond, so Needham has found the nymphs to have various preferred lurking-places in the pond. The damsel-fly nymphs and a few of the more active dragon-fly nymphs clamber among submerged vegetation or inhabit driftwood and submerged roots or brush. The heavier sprawling Libellulid nymphs usually crawl over the bottom or climb over fallen rubbish, while certain other Libellulids and some similar forms occupy the mud or sand of the bottom. The nymphs of one of these latter kinds is described as each scratching a hole for itself and descending into it like a chicken into a dust-bath, kicking the sand over its back and burrowing until all but hidden, only the tops of its eyes, the tips of its treacherous labium, and the respiratory aperture at the end of the abdomen reaching the surface.

After the few weeks or month or year which the nymph requires for its full growth and development it is ready to transform. If in early summer, when the dragon-flies are beginning to appear, one will go out to the dragon-fly pond a little after daylight, he will see this transforming or issuance of the

86

Dragon-flies and Damsel-flies

winged imagoes busily going on. The nymphs crawl out of the water, and up on stones or projecting sticks, or on bridge-piles or the sides of boats, or on the stems of weeds growing by the water’s edge. Here 'they cling quietly,

awaiting the moment when the chi- tinous body-wall shall split lengthwise along the back of the thorax, and the made-over body inside with its damp, compressed wings, its delicate trans¬ parent skin, and changed mouth-parts and legs shall slowly work its way out of the old nymphal coat. The nymphs of some dragon-flies and damsel-flies crawl out among the weeds and grass of the shore for some distance before choosing a resting-place, and none of these will be very readily seen. But careful searching in a place from which winged individuals are occasionally arising will- soon reveal the transforming in all of its stages (Fig. 116). It takes some time for the emergence of the damp, soft imago from the nymphal skin, and some further time for the slow expanding and drying of the wings, and the hardening of the body- wall so that the muscles can safely pull against it. When all this has come about the imago can fly away. But even yet the colors are not fully acquired

Fig. ii6. — The issuance of an adult white tail, Plathemis trimaculata. (After Need¬ ham; natural size.)

Fig. i i 7. — Adult and last exuvia of the whitetail, Plathemis trimaculata. (Natural size.)

and fixed, and these fresh imagoes have an unmistakably new and shiny appearance. They are called teneral specimens. Usually the emergence of nymphs from the pond and the subsequent transforming cease by the middle of the forenoon, and after that one can And only the frail, drying

Dragon-flies and Damsel-flies

87

cast nymphal skins or exuviae, clinging here and there to stones and plant- stems. Attached to these exuviae there may be often noted two or three short, white, thread-like processes. These are the dry chitinous inner linings of the main tracheal trunks of the dragon-fly which were moulted with the outer body-wall. As the main tracheal tubes are really invagina¬ tions of the outer skin, it is obvious that the inner lining of the trachea is continuous with the outer coat (chitinized cuticle) of the body-wall and so is naturally cast off with it.

Although the habits of the adult dragon-flies must be studied out of doors, the nymphs can be brought indoors and kept alive so that their walking and swimming and hiding Fig. i 18. — Adult and last exuvia of the damsel- and capturing of prey, and often Ay, Lesles uncala. (Natural size.)

their transformation into winged imagoes, can be readily observed. In their natural habitat some of these observations are nearly impossible,

and for school-room or private-study aquaria hardly any other animals can be found of more interest to the observer, whether child or grown-up, than the dragon-fly nymphs.

Professor Needham, who has done more and better work in the study of the immature life of dragon-flies than anybody else, gives the following directions for collecting and rearing the nymphs:

“If one wishes to collect the nymphs which lie sprawling amid fallen trash, a garden-rake with which to draw the trash aside, fingers not too dainty to pick them up when they make themselves conspicuous by their active efforts to get back into the water, and a pail of water in which to carry them home, are all the apparatus required.

“A rake will bring ashore those other nymphs which burrow shallowly under the sediment that lies on the bottom, and also a few of those that cling to vegeta¬ tion near the surface; but for getting these latter a net is better. Fig. 119

Fig. i 19. — A home-made water- net for collecting dragon-fly nymphs. (After Needham.)

88

Dragon-flies and Damsel-flies

shows the construction of a good water-net that can be made at home out of a piece of grass-cloth, two sizes of wire, and a stick.

“The best places to search for dragon-fly nymphs in general are the reedy borders of ponds and the places where trash falls in the eddies of creeks. The smaller the body of water, if permanent, the more likely it is to yield good collecting. The nymphs may be kept in any reasonably clean vessel that will hold water. Some clean sand should be placed in the bottom, especially for burrowers, and water-plants for damsel-fly nymphs to rest on. They may be fed occasionally upon such small insects (smaller than themselves) as a water-net or a sieve will catch in any pond. Their habits can be studied at leisure in a dish of water on one’s desk or table.

“The best season for collecting them is spring and early summer. April and May are the best months of the year, because at this time most nymphs

are nearly grown, and, if taken then, will need to be kept but a short time before transforming into adults. And this transformation every one should see; it will be worth a week’s work at the desk; and as it can be appreciated only by being seen, some simple direc¬ tions are here given for bringing the Fig. 120.— A simple aquarium for rear- nymphs t0 maturity. Place them in a

ham.) wooden pail or tub (Fig. 120). If

the sides are so smooth that they cannot crawl up to transform, put some sticks in the water for them to crawl out on. Tie mosquito-netting tightly over the top, or, better, make a screen cover; leave three or four inches of air between the water and the netting; feed at least once a week, set them where the sun will reach them; and after the advent of warm spring weather look in on them early every morning to see what is going on.”

Elsewhere Professor Needham says that nymphs may be fed bits of fresh meat in lieu of live insects. If meat is fed, it must be kept in motion before them, as they will refuse anything that does not seem alive. Some nymphs will take earthworms. Care must be taken to keep cannibalistic kinds apart from others. When the nymphs transform the freshly issued imagoes should be transferred each with its cast skin (exuvia) to dry boxes for a short time, till their body-wall and wings gain firmness and the colors are matured. The imago and its exuvia should always be kept together.

Specimens of the adults for the cabinet should have the wings spread like butterflies and moths (for directions for spreading see the Appendix). The slender and brittle dried abdomen breaks off very easily, and a bristle or fine non-corrosive wire should therefore be passed lengthwise through the body as far as the tip of the abdomen. A couple of insect-pins, inserted

Dragon-flies and Damsel-flies

89

lengthwise one at each end of the body, are used by some. Specimens intended for exchange should not be pinned up, but “ papered,” i.e., put with folded wings into an enclosing little triangular paper envelope made by folding an oblong paper sheet once diagonally and then folding over slightly the two margins.

Fig. 121. — Diagram of venation of wing of dragon-fly. <2, antecubitals; b, postcubitals; N, nodus; P, pterostigma; A, arculus; /, triangle. (After Banks.)

TABLES FOR CLASSIFICATION.

Key to Suborders (Imagoes).

Front and hind wings nearly similar in outline, and held vertically over the back when at rest; head wide and with eyes projecting and constricted at base.

(Damsel-flies.) Suborder Zygoptera. Front and hind wings dissimilar, hind wings usually being much wider at base, and both pairs held horizontally outstretched when at rest; eyes not projecting

and constricted at base . (Dragon-flies.) Suborder Anisoptera.

Key to Suborders (Nymphs).

Posterior tip of abdomen bearing three, usually long, leaf-like tracheal gills.

(Damsel-flies.) Suborder Zygoptera. Posterior tip of abdomen with five, converging, short, spine-like appendages.

(Dragon-flies.) Suborder Anisoptera.

SUBORDER ZYGOPTERA.

Key to Families (Imagoes).

Wings with not less than five antecubital cross-veins (Fig. 121).

Family Calopterygid^e.

Wings with not more than three, usually two, antecubitals (Fig. 121).

Family Agrionidze.

Key to Families (Nymphs).

Basal segment of the antennae extremely elongate . Family Calopterygid^e.

Basal segment of the antennae short, subrotund . Family Agrionid^e.

The family Calopterygidse includes but two genera, Calopteryx, in which the basilar space of the wings is open and the wings themselves are rather broad near the tip, and Hetaerina, in which the basilar space is net-veined and the wings narrow.

Calopteryx maculata (Fig. 122), the most familiar representative in the Eastern States of the first genus, has velvety black spoon-shaped wings,

9°

Dragon-flies and Damsel-flies

Fig. 122. — The black wing, Calopteryx maculata.

(brownish in freshly moulted, or teneral specimens), and a long, slender body, of striking metallic blue or green. The females can be distinguished from the males by their possession of a milk-white pterostigma (Fig. 121). These beautiful “black wings” are found in gentle fluttering flight, usually along 'small streams in woods or meadows. The female lays her eggs “among

the rubbish and mud along the borders of ditches,” and the nymphs found in the ditches and streamlets have the middle one of the three caudal gills flat and shorter than the other two. Kellicott has seen the males of this species fight fiercely with each other. “Two will fly about each other, evidently with con¬ suming rage, when one finally appears to have secured a posi¬ tion of advantage and darts at his enemy, attempting, often suc¬ cessfully, to tear and damage his wings.”

The best known representative of the other genus is a perfect master¬ piece of insect beauty and grace. Entomologists know it as Hetcerina americana (Fig. 123); I suggest that we call it the “ruby-spot,” although only the males bear the gem. The head and thorax of the males are coppery red, the abdomen me¬

tallic green to coppery, and the basal fourth of each of the long, slender, and otherwise clear wings is bright blood-red. In the females the whole body is metallic green, with the basal third of the wings pale yellowish brown. These dam¬ sel-fly beauties are shy and retiring, rarely venturing more than a few feet away from the willow-overhung bank of their favorite swift-running stream. Sometimes hundreds of them come together and cling in graceful festoons to the drooping willow branches. Then they look like strings of rubies, or of warm red flowers or seeds.

The family Agrionidas includes the host of slender-bodied, narrow- and

Fig. 123. — The ruby-spot, Hetcerina americana.

Dragon-flies and Damsel-flies

91

clear-winged true damsel-flies. Most of them are small, and many keep so closely in low herbage or shrubby woodland that they attract little atten¬ tion. A few of the longer-bodied and longer-winged forms, however, fly in the open along the stream-banks or over the ponds. Some are strikingly varied with black and orange or yellow, and all, whether brightly colored or dull, are graceful and charming. There are at least a dozen genera of Agrionids in this country, comprising about seventy-five species, but their classification is too difficult to be undertaken by general students. Damsel- flies deposit their eggs in the tissue of aquatic plants by cutting slits in the stems with their sharp ovipositor. The nymphs are slender and elongate, and can readily be known by the three caudal leaf-like tracheal gills. The nymph stage of these forms is much shorter than with the true dragon-flies, lasting usually probably but a few weeks, or at most two or three months. When ready to transform the nymphs crawl out of the water and into the low herbage on the stream or pond bank. I have seen scores of freshly emerged damsel-flies rising from a few square yards of tall grass near a pond, although it required close search to discover the nymphs, so well concealed were they in the dense tangle.

SUBORDER ANISOPTERA.

Key to Families (Imagoes).

Antecubitals of the first and second rows mostly meeting each other; triangle of fore wings with long axis at right angles to the length of the wings, triangle of hind wing with long axis in direction of the length of the wing.

Libellulid,e.

Antecubitals of the first and second rows not meeting (or running into each other) except the first and another thick one; triangles of fore and hind wings of similar shape (Fig. 121).

Eyes meeting above on middle line of head; abdomen with lateral ridges.

/Eschnid^e.

Eyes just touching at a single point or barely apart; abdomen without lateral

ridges . Cordulegasterid^e.

Eyes distinctly separated; abdomen without lateral ridges . Gomphid^e.

Key to Families (Nymphs).

Under-lip (labium) flat, not concealing most of the face, with jaw-like or oblong side pieces (lateral lobes).

Antennae 7-segmented, tarsi 3-segmented, climbing nymphs. .^Eschnid^e. Antennae 4-segmented, the fourth segment rudimentary; fore tarsi 2 -seg¬ mented; burrowing nymphs . Gomphid^e.

Under-lip (labium) spoon-shaped, covering most of the face, when closed, with nearly triangular side pieces (lateral lobes).

Two stout teeth with a notch between them on the middle lobe of the under¬ lip (labium) . Cordulegasterid^e.

A single median tooth on the middle lobe of the under-lip - Libellulid^e.

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Dragon-flies and Damsel-flies

The family Cordulegasteridae includes only seven species of dragon-flies found in the United States, all belonging to one genus, Cordulegaster. They are large, with eyes barely touching on top of the head, without metallic body-colors, and with clear wings. The nymphs burrow into the sand or vegetable silt on the bottom of shallow places. Thus buried, with only the top of the eyes and tip of the abdomen showing, they remain motionless for a long time, if prey does not come near. “In a dish of sand on my table,” says Needham, “I have had a nymph remain without change of position for weeks, no food being offered it. Let any little insect walk or swim near the nymph’s head, and a hidden labium springs from the sand with a mighty sweep and clutches it.” The imagoes are strong flyers and have the habit of flying back and forth, as on a regular beat, over some small, clear stream.

The family Gomphidae includes six genera, comprising about fifty species in our country. They are mostly large forms, clear-winged and with bodies striped with black and green or yellow. They are readily distinguished by the wide separation of the rather small eyes. The abdomen is stiff and spike-like. The eggs, held in a scanty envelope of gelatin, are deposited by the repeated descent of the flying female to the water of a clear pond or flowing stream, the tip of the abdomen first striking the surface. The gelatin dissolves and the eggs, scattering, sink to the bottom and become hidden in the silt. The nymphs are active burrowers, capturing their prey either on or beneath the surface of the bottom silt. The adults often