Part 5

Legs fitted for running, as in fig. 41, without Suborder large pincers at their ends; mouthparts situated Mallophaga near the middle of under side of the head and fitted for chewing. Occurring on birds and mammals. The chewing lice Legs fitted for clinging to hairs, each leg Suborder Anoplura 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 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

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.

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.

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.

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.

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.

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.

Mecoptera Scorpionflies

Insects typically with two similar pairs of delicate wings, each wing with a network of veins. In repose the wings are laid either tentlike over the back or almost flat. The mouthparts are fitted for chewing and usually are lengthened into a beaklike structure, as in _Panorpa chelata_ Carpenter, fig. 60. The larvae, seldom found, live in damp woods. The adults of most winged species occurring in Illinois are about 0.5 inch long. They are active in early summer in shady woods, flying through the undergrowth. Adults of the genus _Boreus_ are smaller and they have very short, veinless wings. They emerge in the winter and early spring; these little metallic black insects often hop around on late winter snow. In certain genera, the adult male genitalia form a bulb-like structure at the end of the body, as in fig. 60. This structure is harmless but, because it resembles a scorpion's sting, insects of these genera are given the name scorpionflies.

Trichoptera Caddisflies

Insects with two pairs of wings, poorly developed mouthparts of the chewing type, and long antennae; without tails on the posterior end of the body. In repose, the wings are held rooflike over the body and have only a moderate number of longitudinal veins, which are not connected by crossveins into any resemblance of a network. Neither body nor wings are covered with scales. The larvae are wormlike and they live in streams, ponds, and lakes. Many of them build cases of sticks, stones, or sand and move about with only the front end of the body protruding from the case. When disturbed, the larvae withdraw completely into the cases and are then very difficult to see. The adult fly and larva of _Rhyacophila fenestra_ Ross illustrate this order, figs. 61 and 62. In many aquatic situations, caddisflies are the predominant small animal life and are an important factor in fish food economy. Also, they are stream pollution indicators.

Lepidoptera Butterflies, Moths

Insects typically with two pairs of wings, with long antennae, and with mouthparts forming a long sucking tube. The body and wings are covered with a dense mass of scales, which are characteristic of this order, fig. 63. The young are known as caterpillars or grubs. The larval stage in this order is well exemplified by the fairly smooth, cylindrical caterpillar of the fall armyworm, _Laphygma frugiperda_ (Smith), fig. 64. Some other larvae are hairy; still others are sluglike.

To this order belong not only a very large number of species, but also a very large number that are especially injurious to agriculture. These include such species as the codling moth, cabbage moth, butterflies, the entire cutworm group, and a host of others. In addition, the various clothes moths, which are a constant source of loss to householders, and various species of meal moths, which cause tremendous damage to stored grain every year, are members of this order.

In one group of moths, there are clear "windows" on the wings, but these are always surrounded by areas or lines of scales. A few species of the Lepidoptera are very odd in having wingless females. Examples are the bagworms and some of the cankerworms. In these species, however, the body of the female is densely clothed with scales, which will serve to identify her as one of the Lepidoptera.

The habits of Lepidoptera larvae are very diverse. Most of these larvae are leaf eaters, but some bore into trunks of trees and stems of herbaceous plants. Some of the small ones mine within leaf tissue, others live in the ground, where they eat roots, and a few are aquatic, living in clear, rapidly flowing streams.

Diptera Flies, Mosquitoes, and Their Allies

Insects with only one pair of wings, each wing with a limited number of veins. Other characters of the order, including antennae and mouthparts, are extremely varied. Most immature stages are wormlike or maggot-like. They live in protected situations, such as within the tissues of a plant, in water, in leaf mold, or in the tissues of animals. A typical life cycle is that shown for the house fly, _Musca domestica_ Linnaeus, fig. 65. The ubiquitous house fly is undoubtedly the best known representative of this order. It is also one of the most persistent and dangerous insect pests, being a possible carrier of many diseases.

Mosquitoes, punkies, black flies, and horse flies are likewise well known members of this order. In addition to economic forms, the order Diptera includes midges, crane flies, bee flies, robber flies, bluebottle flies, and a great assortment of other kinds of insects. Interesting are the bee flies, which mimic other insects such as honey bees, bumble bees, and wasps to an extent that wins them immunity from the attention of many beginning collectors.

Siphonaptera Fleas

Wingless insects that evolved from folding-wing insects; conspicuously flattened from side to side; with stout spiny legs, and with numerous spines over the body; without conspicuous antennae or tails or a forked posterior appendage like that of the springtails; usually hard; ranging in color from yellowish brown to almost black.

The human flea, _Pulex irritants_ Linnaeus, and a widespread Illinois rat flea, _Nosopsyllus fasciatus_ (Bosc), are shown in fig. 66.

All the fleas, which feed on the blood of birds and other animals, have sucking mouthparts. They are powerful jumpers. The young stages are slender, white larvae, fig. 67, which live in the nests of various animals; these larvae are seldom collected. The fleas are found on the animals themselves or around their nests. Several species of fleas, including the cat and dog flea, the human flea, and the rat fleas, attack man. One of the rat fleas, _Xenopsylla cheopis_ (Rothschild) is the common transmitter of the organism causing bubonic plague.

RELATIVES OF INSECTS

There are many small animals that belong to the same general group as insects and that are frequently collected with them. Spiders, centipedes, and amphipods are a few of many examples of such animals. Together with insects, they form the animal phylum called Arthropoda, characterized by having segmented bodies and jointed legs. A brief description is included here of the common groups of these insect relatives found in Illinois.

Isopoda Sowbugs, Pillbugs