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.