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.)