Part 9

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.

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:

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