Fig. 19.—Diagram of a typical adult winged insect. This illustrates many of the parts that are useful in identifying these creatures. (Drawing adapted from R. E. Snodgrass.)
- HEAD
- Antenna
- Ocelli
- Eye
- THORAX
- 1
- Front leg
- 2
- Front wing
- Middle leg
- 3
- Hind wing
- Hind leg
- ABDOMEN
- Cercus
Five existing orders of insects, all found in Illinois, are representative of the primeval wingless insects. In all five, the individual molts at intervals, even after becoming adult and sexually mature, and the old and young are extremely similar. Three of the primitive orders, the campodeids, proturans, and springtails, belong to a specialized early branch of the insect family tree, fig. 18, in which the cheeks have grown forward to form a pouch surrounding the mouthparts. In the other two primitive orders, the bristletails and silverfish, the mouthparts are in a normally exposed condition, but the legs are larger and the insects are rapid runners.
From one of these ancestral, silverfish-like insects arose a form in which wings evolved. In birds and bats, the wings are converted front legs with membranes or feathers attached to form planing or flying surfaces. In insects, on the other hand, the wings are outgrowths of the edge of the body where the sides and top come together, fig. 19. The wings probably began as side flanges of the thorax and permitted a certain amount of planing. Whatever their origin, two pairs of flying wings did evolve, one pair on the second and another on the third segment of the thorax.
In the early winged forms, the wings could not be folded back in repose over the body, but were held out from the sides like airplane wings or together above the body like sails. Two living orders of insects represent this type, the mayflies and the dragonflies. In both of these, as in other winged insects, the wings form as small pads during the early stages of the individual; then at a final molt they are unfolded as functional units. In the mayflies, one more molt occurs after the wings are formed; in this molt the old outside covering of the wings is shed along with that of the rest of the insect. In all other winged insects no molt occurs after the wings are formed and the individual becomes sexually mature.
Insects having erect, nonfolding wings were abundant some 300 million years ago. Fossil remains of many of these early forms have been found in the Mazon Creek area in Illinois, fig. 20.
From one of these early winged types a form evolved in which the wings could be folded compactly over the body; this form gave rise to a great many of our present-day insects. In the first insects that evolved from this form the wing pads of the immature stages, called nymphs, grew as external and often inconspicuous flaps held close to the body. These primitive insects comprise three distinctive groups, characterized mainly by differences in leg and body structure. One group contains the cockroaches, grasshoppers, and their allies; the second includes only the stoneflies; and the third group includes the barklice, true lice, bugs, and their allies.
Fig. 20.—An insect fossil from an iron nodule or concretion found at Mazon Creek, Illinois; hind leg of an ancestral mayfly, Lithoneura mirifica Carpenter. Actual length of wing about one-half inch. This fossil represents an insect which lived during the Pennsylvanian period, about 250 million years ago. (Photograph courtesy of Illinois State Museum.)
One of the primitive lines of wing-folding insects, possibly an offshoot from the base of the barklouse-bug line, evolved into a distinctly different type in which the wing pads of the immature stages developed internally and appeared as external pads only in the stage before the adult form. The type was characterized by a marked difference of appearance between the various stages of the life history; these stages have been given distinctive names. The first immature stage, which is without external wing pads, is called a larva; the single stage with the external wing pads is called the pupa; and the final winged, sexually mature stage is called the adult. The larva is essentially a growing stage, the pupa is a quiescent stage of internal reorganization, and the adult is the egg-producing stage. This type of insect gradually gave rise to the orders which now contain the largest number of species, including the beetles, moths, and flies. In many lines of this neuropteroid branch, as it is called, the larva has become adapted to a mode of life quite different from that of the adult. Many fly larvae, for example, live in rotting organic material or live as parasites within the tissues of other kinds of insects, whereas the adult flies often feed at flowers on pollen and nectar, visiting the site of the larval habitat only to lay eggs. As a result of this type of evolution, members of the neuropteroid orders exhibit many bizarre and complicated life histories.
Occasionally certain groups of winged insects evolved new types which had small wings or were wingless. The new types resulted because the groups were subjected to environmental situations where wings were of little survival value. Within the groups, individuals with smaller wings were favored; they survived and reproduced in greater numbers than other individuals. Over many generations then, the wings in some groups became very small or were entirely lost. Sometimes this loss of wings occurred in all the adult forms, as in the fleas. Individuals of only one sex may be wingless, as are the females of two Illinois moths, one of which produces bagworms and the other cankerworms. In two groups, the termites and the ants, a wingless worker or soldier caste is produced; in these groups the normal adults which swarm and reproduce are fully winged. These winged forms establish new colonies.
Wings were lost in the evolutionary development of two insect groups that became parasites of warm-blooded animals, both birds and mammals. Each of these insect groups developed into a large, distinctive order. One order, the true lice, evolved from the barklice, and the other, the fleas, evolved possibly from a primeval fly group. Although these two orders, the lice and the fleas, are without wings, the structure of their bodies and their life histories provide adequate testimony of their evolutionary affinities.
The following synopsis of Illinois insects treats the various kinds in the sequence in which we believe they evolved, from the extremely primitive bristletails to the highly specialized flies.
HOW TO IDENTIFY SPECIMENS
As an aid to the beginner in making preliminary identification of his specimens and also as an aid in arranging his collection, a short descriptive synopsis of the orders of living insects is given below. In this description are noted the most distinctive features of the common insects occurring in Illinois. There are rare and obscure forms, seldom met by the collector, that require a more technical key for their identification; for these the collector will need to consult some of the more nearly complete books listed on page 70. The collector will find, however, that this synopsis will afford a beginning for his classification of the common forms.
Various characters are used to identify an insect to family, genus, and species. Among these characters are the antennae, wings (if present), legs, and mouthparts. Frequently important for identification are such minute details as hair or scales covering the body or wings and the texture of these parts. In most cases good microscopic equipment is necessary to see clearly the characters used in the diagnosis of insects.
SYNOPSIS OF ILLINOIS INSECT ORDERS
Of the 28 orders of insects recognized in North America, 26 have been collected in Illinois. The two orders not found here are the Embioptera or webspinners, a tropical and subtropical order, and the Raphidiodea or snakeflies, which occur in the western mountainous region of the continent.
The Illinois fauna thus contains a remarkable variety of insects, including forms such as the bristletails, mayflies, and cockroaches, which are practically “living fossils” of insects that lived hundreds of millions of years ago.
Primitive Wingless Insects
Only five orders of primitive wingless insects are known; species of each order occur in Illinois. These orders represent the stages in insect evolution before wings had appeared.
Fig. 21.—Diplura. A campodeid belonging to the genus Campodea, found under stones in moist places. Actual length of adult about 0.1 inch. (Drawing from E. O. Essig.)
Fig. 22.—Protura. Acerentulus barberi, a proturan found on sticks and leaves in the leaf mold of forests. Actual length of adult about 0.02 inch. (Drawing from H. E. Ewing.)
Diplura
Campodeids, Japygids
Small, wingless, fragile, blind, whitish insects that run fairly rapidly. They have long antennae and either two fairly long tails or a pair of forceps-like structures at the end of the abdomen. They are terrestrial and are found chiefly under stones in humid and shady situations. Fig. 21 shows a common campodeid, a species of Campodea, occurring commonly in Illinois.
The Diplura feed on fungi and other soil microorganisms. Although they are found most frequently under stones, they live also in the soil and in matted leaves or duff on the floor of woods. About a dozen species of Diplura occur in Illinois.
Protura
Proturans
Minute, wingless, blind insects that never grow to more than 0.05 inch long. They have no antennae and use the front legs to some extent for feeling. They are terrestrial and are found inhabiting dead twigs and leaves on the forest floor. Fig. 22 shows Acerentulus barberi Ewing, a member of a genus which occurs in many localities in Illinois. Only a few species of proturans have been taken in the state.
Collembola
Springtails
Small, wingless insects that jump and crawl when disturbed. They have short antennae and usually a springing structure on the under side near the posterior end of the body. They live in moist places and are abundant under leaf mold and similar material. Illustrated in fig. 23 is Achorutes armatus Nicolet, which often becomes a major pest in mushroom cellars and greenhouses.
About a hundred different species of Collembola occur in Illinois; they include some of our smallest insects. A few never grow longer than 0.007 inch; the largest approach half an inch in length. These hardy animals are active all year and are surprisingly resistant to cold. Certain species occur on snow in winter. In Illinois a small, bluish gray species, Podura aquatica Linnaeus, is found on the surface of still water at the margins of ponds and small streams.
Microcoryphia
Bristletails
Wingless, somewhat cylindrical insects that run and jump with extreme rapidity. They have long antennae and three long tails. The under side of the abdomen bears several pairs of short projections called styli, which are vestiges of abdominal legs. Bristletails live in rocky places or in ground cover. A type occurring in some parts of Illinois is shown in fig. 24. It often occurs on rocky exposures, where it resembles the lichens and is difficult to detect.
Fig. 23.—Collembola. A, Isotoma andrei; B, Achorutes armatus; C, Neosminthurus clavatus. A and C are found in woodland leaf molds; B is frequently abundant in commercial mushroom cellars. Actual length of adults ranges from 0.03 to 0.05 inch. (Drawings A and C after Harlow B. Mills.)
Fig. 24.—Microcoryphia. A bristletail belonging to the genus Machilis, often found on lichen-covered, shaded rocks. Actual length including tail is sometimes 0.5 inch. (Drawing after R. E. Snodgrass.)
Fig. 25.—Thysanura. Thermobia domestica, a common Silverfish. Actual length about 0.3 inch.
Thysanura
Silverfish
Wingless, flat insects that run rapidly. They have long antennae and three long tails. They are terrestrial and are commonly found in dwellings. Fig. 25 shows one of the common Silverfish, Thermobia domestica (Packard); it frequently eats book bindings and other starchy materials. Some out-of-door rare forms live in the soil and are seldom collected.
Primitive Winged Insects
The primitive winged insects cannot fold their wings, which in repose are held erect over the body or straight out from the sides, as illustrated in figs. 26 and 29. Although many types of these insects lived in bygone ages, only two orders have survived to the present. Both occur abundantly in Illinois.
Ephemeroptera
Mayflies
A group of insects in which the nymphs or young live in streams and lakes; the adults are found along the edges of the streams or lakes from which they have emerged. Mayflies are unique in that the full-grown nymphs molt into winged insects that are not quite mature and that molt again, usually the next day, when they emerge as fully mature adults. The nymphs are varied in shape and have short antennae, long legs, which are often flattened, and three tails at the end of the body. The adult flies have very long front legs, short antennae, practically no mouthparts, usually two pairs of wings, and two or three long tails. When a mayfly is at rest, the wings are held together above the body. Hexagenia limbata (Serville), figs. 26 and 27, is one of the very common Illinois mayflies and is an important factor in the food economy of many fish.
Mayflies, formerly called Plectoptera, together with stoneflies, caddisflies, and midges, constitute a very large portion of the life of our lakes and streams; all four groups are important as fish food.
Odonata
Dragonflies, Damselflies
Another order in which the nymphs develop in streams, lakes, or ponds, and in which the adults are aerial. The nymphs have short antennae, long legs, and either a stout body with no tail, as in Anax junius (Drury), fig. 28 (dragonfly nymph), or a slender body with three large leaflike gills projecting from the end of the body (damselfly nymph). A most distinctive feature of this order is an extensile, highly modified lower lip that fits like a mask over the face of a nymph. The lower lip is hinged to extend forward and seize the small animals upon which the nymph lives. The adults are large, often beautifully colored, as is the Tramea lacerata Hagen, fig. 29. They have chewing mouthparts and two pairs of large wings, very finely and intricately netted with veins.
Fig. 26.—Ephemeroptera. Hexagenia limbata, the adult form; this mayfly is also called shadfly or willowfly. Mayflies sometimes emerge in great swarms and congregate in piles around bridge or city lights. Actual length about 1.0 inch.
Fig. 27.—Ephemeroptera. Hexagenia limbata, the nymphal form of the mayfly in fig. 26; in this stage the mayfly lives in water, emerging when full grown. Actual length about 1.0 inch.
The order is divided into two types; the adult flies are told apart as follows:
| Body stout, wings broad at base, the front and hind wings different in shape. Strong fliers. Dragonflies | Suborder Anisoptera |
| Body slender, wings narrowed at base, the front and hind wings similar in shape. Weaker fliers than dragonflies but nonetheless elusive. Damselflies | Suborder Zygoptera |
Fig. 28.—Odonata. Nymph of Anax junius, a dragonfly widely distributed in Illinois. Actual length of full-grown nymph about 2.3 inches. (Drawing courtesy of C. O. Mohr.)
Fig. 29.—Odonata. Tramea lacerata, a dragonfly commonly found near ponds and drainage ditches in Illinois. Wingspread about 3.2 inches. (Drawing courtesy of C. O. Mohr.)
Folding-Wing Insects
Almost all insects in this category can fold their wings in repose back over their bodies, as illustrated in fig. 31. A few kinds, notably some of the moths and butterflies, have lost this wing action and in repose hold their wings erect. In some of these kinds, the male is winged and the female is wingless; in others, certain generations may be wingless and others winged; and, in still others, the species may be wingless in all stages. No members of the orders of folding-wing insects molt after becoming winged or sexually mature.
Fig. 30.—Cursoria. Supella supellectilium, the brown-banded cockroach. Actual length about 0.6 inch. (Drawing courtesy of C. O. Mohr.)
Fig. 31.—Cursoria. Stagmomantis carolina, a praying mantis. Common in southern and central Illinois. Actual length of adult about 1.5 to 2.0 inches.
Fig. 32.—Cursoria. Diapheromera femorata, a walkingstick insect. This insect lacks wings. Actual length about 3.0 inches. (Drawing courtesy of C. O. Mohr.)
Cursoria
Cockroaches, Mantids, Walkingsticks
An order that includes three groups of terrestrial insects, each group markedly different in appearance from the others: (1) rapidly running insects usually having two pairs of wings, each with a dense network of fine veins, the front pair of wings thick and leathery, fig. 30 (cockroaches); (2) winged insects having long, grasping front legs, fig. 31 (praying mantids); and long, wingless insects resembling sticks, fig. 32 (walkingsticks). The mouthparts are fitted for chewing. The young look and act like the adults except that they do not have wings. The cockroaches are omnivorous, feeding chiefly on organic foods rich in carbohydrates, or on fungus growth. Cockroaches are among our most persistent indoor pests, eating a wide variety of domestic foods. The praying mantids feed on other insects, which they capture in their enlarged front legs. The walkingsticks eat leaves. The cockroaches and mantids lay eggs that are glued together and form pods or capsules, each containing 30 or more eggs. The walkingsticks lay their eggs singly.
Fig. 33.—Isoptera. Reticulitermes flavipes, the commonest kind of termite found in Illinois: A, first form queen with wings spread, many times natural size (this is the form that lays eggs); B, worker nymph, natural size; C, first form queen, approximately natural size, with wings placed in their natural resting position. (Drawing courtesy of C. O. Mohr.)
Fig. 34.—Orthoptera. Melanoplus bilituratus, the migratory locust, a common Illinois grasshopper. Actual length about 1.0 inch.
Isoptera
Termites
Fragile or soft insects with chewing mouthparts. The mating forms are dark brown and have two similar pairs of wings; both pairs are delicate and have a fine network of veins. The workers are white and soft bodied. Termites, which live in colonies in wood, are also called “white ants,” although they are not true ants. The common native species in Illinois is Reticulitermes flavipes (Kollar), fig. 33, which lives in rotten logs and is destructive to buildings of wooden construction throughout Illinois; it is most destructive in the southern part of the state.
Fig. 35.—Orthoptera. Ceuthophilus maculatus, a wingless cave cricket. Crickets of this kind are found in caves, under rocks, and in basements. Actual length about 1.0 inch.
Fig. 36.—Dermaptera. Labia minor, an earwig frequently abundant in Illinois. Actual length of adult about 0.2 inch.
Orthoptera
Grasshoppers, Crickets
Terrestrial insects usually with two pairs of wings, each wing with a very fine, dense network of veins, the front pair thick and leathery, the hind pair delicate and fanlike. The mouthparts, fitted for chewing, have stout mandibles. The young look and act like the adults but do not have wings. This order includes all the grasshoppers, crickets, and katydids. Fig. 34 shows the migratory locust or grasshopper, Melanoplus bilituratus (Walker). Adults of several of the groups of Orthoptera never develop wings. These include such odd forms as the cave crickets, exemplified by Ceuthophilus maculatus (Harris), fig. 35.
Dermaptera
Earwigs
Insects with two pairs of wings, the front pair forming short, hard covers, the second pair large, membranous, many-veined, and in repose folded intricately beneath the front pair. The abdomen ends in a pair of pincer-like structures. A common Illinois form is Labia minor (Linnaeus), shown in fig. 36. Of the half-dozen species known from Illinois, all but one were originally from Europe or Asia. Earwig females lay eggs in chambers in the ground and guard them.
Fig. 37.—Plecoptera. Isoperla confusa, one of the typical stoneflies found in Illinois; adult form. Actual length about 0.8 inch. Illinois stoneflies range in length from 0.25 inch to 1.5 inches.
Fig. 38.—Plecoptera. Isoperla confusa; the nymph of the species shown in fig. 37. The nymph lives in streams. Actual length about 0.6 inch.
Plecoptera
Stoneflies
Insects that pass the young or nymphal stage in streams. They have slender, soft bodies and long tails; they move about rapidly. The adults are terrestrial in habit and occur along streams. In most species, the adults have two pairs of wings that are folded flat over the back; the number of crossveins varies from many to few. The antennae are long; the mouthparts are of the chewing type but greatly reduced. Of exceptional interest are stonefly adults that emerge in winter and are active from November through March. The winter forms can often be collected on bridges. Figs. 37 and 38 illustrate a spring species, Isoperla confusa Frison.
Zoraptera
Zorapterans
Small, whitish insects, about a twelfth of an inch long, that run rapidly. They live in small colonies in rotting sawdust, in rotten logs, and under the bark of stumps. They have fairly long antennae, chewing mouthparts, and a pair of short, inconspicuous tails. Most members of a colony are wingless, but occasionally there occurs a darker specimen having two pairs of wings. These wings have only a few veins. In Illinois only a single rare species has been found; it is called Zorotypus hubbardi Caudell, fig. 39.
Corrodentia
Booklice, Barklice
Small, rounded or flattened insects, rarely a quarter-inch long, usually about 0.13 inch. In many species, adults have two pairs of wings, which have only a few zigzagging veins. Winged forms, such as Psocus striatus Walker, fig. 40, are found in crevices of bark and on dead leaves. Common species found in houses and on stored grain are usually wingless and louselike, similar in general appearance to fig. 41. Corrodentia eat fungus growth on bark, dead leaves, moldy grain, damp books, and similar materials. Some of the outdoor species become very abundant on drying corn leaves during autumn and may breed in immense numbers. They do little harm, feeding chiefly on fungus strands.
Phthiraptera
Chewing Lice, Sucking Lice
Wingless, blind, flattened insects with short antennae, short legs, inconspicuous mouthparts, and no tails on the posterior end of body. They are found exclusively on the bodies of birds and other warm-blooded animals. The young have the same general shape and habits as the adults and are found with them. Illinois species of lice belong to two distinct suborders, which may be differentiated through use of the following key:
Fig. 39.—Zoraptera. Zorotypus hubbardi, the only zorapteron recorded from Illinois. The specimen on the left is a winged adult female; the specimen on the right is a wingless adult female. Actual length of adults about 0.08 inch.
Fig. 40.—Corrodentia. Psocus striatus, a common bark louse found on many trees. Actual length 0.2 inch.
Fig. 41.—Phthiraptera. Suborder Mallophaga. Cuclotogaster heterographus, a chewing louse found on the heads of poultry. Actual length about 0.1 inch.
Fig. 42.—Phthiraptera. Suborder Anoplura. Haematopinus asini, the blood-sucking horse louse. Actual length 0.1 inch.
| Legs fitted for running, as in fig. 41, without large pincers at their ends; mouthparts situated near the middle of under side of the head and fitted for chewing. Occurring on birds and mammals. The chewing lice | Suborder Mallophaga |
| Legs fitted for clinging to hairs, each leg ending in a large pincer, as in fig. 42; mouthparts retracted within head, consisting of a set of thin, needle-like parts fitted for sucking blood. Normally occurring only on mammals. The sucking lice | Suborder Anoplura |
Suborder Mallophaga.
Individuals of many species of chewing lice move about with considerable rapidity. Many of them are very prettily banded and colored, as is the chicken head louse, Cuclotogaster heterographus (Nitzsch), fig. 41. Anyone who has worked with domestic fowls or animals has seen members of this order scurrying among the feathers or hair. These insects feed on what they can chew from the surface of the skin and in some cases are known to injure their hosts.
Suborder Anoplura.
The sucking lice are sluggish insects that usually cling to hairs. Human lice are often found clinging to clothing. Various species occur on native and domestic species of mammals in Illinois. Fig. 42 shows the horse louse, Haematopinus asini (Linnaeus).
Thysanoptera
Thrips
Fig. 43.—Thysanoptera. Thrips tabaci, onion thrips. Actual length less than 0.1 inch.
Small, active insects, usually about 0.1 inch long, rarely a quarter-inch long, very slender, usually each with two pairs of narrow wings and with the under side of the head forming a sharp, conelike sucking structure. Each wing has a long fringe on the hind margin; each front wing may have one or two veins running the length of the wing. The young of these insects are somewhat similar to the adults but are softer bodied. Fig. 43 shows an adult of Thrips tabaci Lindeman, the onion thrips. Thrips suck the juice from plants. Because of their minute size, they are seldom noticed, but they can be collected in large numbers from blossoms of almost any plant. A few species of thrips, such as the onion thrips and the privet thrips, attack agricultural or horticultural plants and inflict considerable damage. A few species occasionally bite human beings.
Hemiptera
True Bugs and Their Allies
Insects usually with two pairs of wings and with the mouthparts formed for sucking. The order contains two distinct suborders, the Heteroptera and the Homoptera. All species of Hemiptera in North America fall readily into one suborder or the other, but certain species in other parts of the world are intermediate between the two suborders.
Fig. 44.—Hemiptera. A typical stink bug of the family Pentatomidae, showing attachment of beak and arrangement of wings. Actual length about 0.4 inch.
In the suborder Heteroptera, containing the stink bugs, the chinch bugs, and their allies, the beak is attached to the under side of the front part of the head; the base of the front pair of wings is hardened, and only the apical portion is membranous or delicate; the entire hind pair is delicate. In repose, the wings are folded over and flat against the body, the hind pair underneath. These characters are shown in fig. 44, which pictures a stink bug belonging to the family Pentatomidae. The young have the same general appearance and habits as the adults, but they lack wings. This suborder includes many common kinds, such as the water bugs, the water striders (these seldom develop wings even in the adult stage), the ambush bugs, and the lace bugs, as well as the stink bugs and the chinch bugs. The chief pest of this group is the chinch bug, Blissus leucopterus (Say), fig. 45. Other pests include many kinds of plant bugs, of which Lygus lineolaris (Beauvois) is shown in fig. 46. The bed bugs, another group never developing functional wings, also belong in this suborder.
Fig. 45.—Hemiptera. Blissus leucopterus, the chinch bug. Actual length about 0.1 inch.
Fig. 46.—Hemiptera. Lygus lineolaris, the tarnished plant bug. Actual length about 0.2 inch.
Fig. 47.—Hemiptera. Anuraphis maidiradicis, the corn root aphid. The form at the left is the winged form; that at the right is the wingless form. All of the plant lice have these two forms. This species, as well as other kinds of plant lice, is frequently attended by ants, which feed on the honeydew produced by the aphids. Actual length less than 0.1 inch.
Members of one family, the Reduviidae or assassin bugs, prey on other insects. A few species called kissing bugs, some of them an inch long, occasionally attack people, inflicting an extremely painful bite and causing considerable bleeding.
Fig. 48.—Hemiptera. Aspidiotus perniciosus, the destructive San Jose scale. The scale is cut away on upper specimen to show insect proper beneath. Diameter less than 0.1 inch.
Fig. 49.—Hemiptera. Empoasca fabae, the potato leafhopper. This species is pale green. Some species are distinguished by bright red or yellow markings. Actual length about 0.1 inch.
Fig. 50.—Megaloptera. The larva of a species of Sialis, an alderfly. This form is aquatic. Actual length 0.7 inch.
Fig. 51.—Megaloptera. The adult of Sialis mohri, an alderfly. Other members of this order reach a length of 1 or 2 inches. They are mostly black, black and white, or mottled gray in color. Actual length 0.5 inch.
The suborder Homoptera contains the cicadas, aphids, and their allies. All these insects have sucking mouthparts, but in each the beak is attached at the back of the head instead of the front of the head as in the suborder Heteroptera. In many species of the Homoptera, each individual has two pairs of wings, both of which are membranous. Probably as many species are without wings, however, as with them. The nymphs are in most respects similar to the adults. Sexual characters, and in some forms wings, gradually develop as the insects approach the adult stage, when development is complete.
Fig. 52.—Neuroptera. Chrysopa nigricornis, a green lacewing. When handled, members of this genus give out a very penetrating and disagreeable odor. Actual length 0.6 inch.
Fig. 53.—Neuroptera. A larva of the genus Chrysopa. This form uses the long jaws to impale aphids and suck their body juices. Actual length 0.5 inch.
This suborder contains a large number of economic pests, including scale insects and leafhoppers, as well as many aphids. In many species of aphids each insect has a pair of tubular structures near the end of the body; these are called cornicles and can be seen in fig. 47, showing the corn root aphid, Anuraphis maidiradicis (Forbes). In most species of scale insects each individual produces a tough scale, which covers and protects its delicate body, as in fig. 48, showing the destructive San Jose scale, Aspidiotus perniciosus Comstock. Leafhoppers of many kinds, such as Empoasca fabae (Harris), fig. 49, are among the destructive pests of beans, potatoes, grapes, apples, and other plants. The treehoppers, spittlebugs, and lanternflies also belong to this suborder.
Megaloptera
Alderflies, Dobsonflies
In this and in the following orders of insects, the life history includes four distinct stages, the egg, the larva, the pupa, and the adult. In the Megaloptera, which include alderflies and dobsonflies, the larvae are caterpillar-like or grublike, and the pupae represent a transformation stage in which the tissues of the larvae are converted to those of the adults. The larvae never have external wing pads; in winged species, these pads first appear externally in the pupae. The adults have long antennae, two similar pairs of net-veined wings, and chewing mouthparts. They are moderately strong fliers. The larvae, fig. 50, live in streams and lakes; when fully grown they migrate to dry land and pupate in the ground or under the bark of rotten logs.
Typical of the appearance of Illinois alderflies is the adult of Sialis mohri Ross, shown in fig. 51. Well known to the fisherman is the hellgrammite, the tough, ferocious, leathery larva found under rocks in streams and prized for bait. This larva matures into the large dobsonfly, Corydalis cornuta (Linnaeus), which often attains a wingspread of 4 inches.
Neuroptera
Lacewings and Their Allies
Insects with two pairs of wings, both pairs about the same size and shape and intricately netted with veins; antennae long and slender, mouthparts fitted for chewing, posterior end of body without tails. The green lacewings, including Chrysopa nigricornis Burmeister, fig. 52, are our commonest members of this order. The young or larvae of this order are entirely unlike the adults and are somewhat grublike in form. The aphid lion, the interesting larva of Chrysopa, fig. 53, is frequently collected by the sweeping method. Another interesting larva of this order is the doodlebug or ant lion, of Huckleberry Finn fame. The adult insects that mature from these ant lion larvae are very similar in appearance to the chrysopids or lacewings. The larva of each of these insects sinks its long, sharp, curved mandibles into the body of its prey and sucks out the body juices. The female Chrysopa has the curious habit of forming a long, slender stalk under each egg; the bottom of the stalk is fastened to the upper side of a leaf. The stalks are thought to have the effect of keeping the first larvae of a hatch from devouring the eggs placed nearby.
When the larva is mature, it spins a globular, silken cocoon or cell around itself and in this changes into the pupal, or quiescent, stage. While the pupa itself does not appear active, within it the larval tissues are reorganized into the structures of the adult, and the final growth of the wings and reproductive organs occurs. When this change is completed, the adult insect emerges from the cocoon.
Fig. 54.—Coleoptera. Copris minutus, one of the scarab beetles. The drawing shows one of the elytra upraised and illustrates the method of folding the hind pair of wings under the elytra. Actual length 0.4 inch.
Fig. 55.—Coleoptera. A weevil belonging to the genus Curculio, which feeds on nuts and acorns. In this genus the beak is exceptionally long. In most of the Illinois weevils the beak is shorter and stouter. Actual length 0.4 inch.
Coleoptera
Beetles, Weevils
Insects with two pairs of wings, the second pair delicate and folded under the first pair, which are hard and thickened and folded back against the body, touching each other along the midline to form a hard shell, as shown in Copris minutus (Drury), fig. 54. The upper wings are not used for locomotion, but form part of the body armor and are called elytra. In most beetles they cover the entire posterior part of the body; in many others they are abbreviated and cover only part of the abdomen. The immature stages of the beetles are wormlike or grublike and have a great variety of food habits. Some of them defoliate plants, others attack roots, and still others feed on other insects.
A great many of the serious insect pests, including kinds that attack field crops, stored products, and household goods, are beetles. Beetles of one group having the front of the head produced into a snoutlike structure, as in the genus Curculio, fig. 55, are called weevils or snout beetles. This group has maggot-like larvae and contains many of our worst pests, such as the plum curculio, cotton boll weevil, alfalfa weevil, and clover weevil. Bizarre and striking forms occur in many beetle groups, notably among the scarab and long-horn beetles. The largest in Illinois is the rhinoceros beetle, Dynastes tityus (Linnaeus); the males (one shown on the cover of this circular) have long projections on both head and thorax; the larvae live in rotten wood.
Tree-boring beetle larvae are destructive to many orchard, ornamental, and native trees. These include chiefly the round-headed borers, adults of which are long-horn beetles; flat-headed borers, adults of which are metallic wood borers; and engraver or shot-hole types, adults of which are small and bullet shaped and are called bark beetles.
In a few families of beetles, both the adults and larvae are fitted for aquatic life. Well known among these are the shining whirligig beetles.
Hymenoptera
Bees, Wasps, Ants, Sawflies
Insects typically with two pairs of wings; antennae of various lengths; chewing mouthparts; without tails. A typical member of this group is the wasp Vespula maculata (Linnaeus), fig. 56. Many adult members of the group are atypical in that they lack wings; these include all the true ants, fig. 57, which are without wings except for the sexual forms produced at the time of the nuptial flights. Forms of one species, Lasius interjectus Mayr, are shown in fig. 58. The wings, when developed, are without scales; the venation is much less extensive than in the Neuroptera; and the hind wings differ in shape and size from the front wings. The young stages of the Hymenoptera are caterpillar-like or grublike, entirely different from the adults.
This very large order includes such well-known forms as the bees, as well as the wasps and the ants, mentioned above. In addition, it includes the sawflies, whose caterpillar-like larvae are extensive defoliators of a large number of native and cultivated plants and shrubs; the large and varied groups of parasitic wasps that exert great influence in the natural control of a tremendous number of other insects; and a large number of gall-making wasps, whose galls are especially conspicuous on oak trees. A parasitic wasp of the genus Opius is shown in fig. 59. The parasitic wasps are extremely diverse in size, shape, and habits. They range in size between 0.02 and 2.0 inches.