Part 10

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.