Insects are among the rarest of fossils, yet more than 130 different kinds have been described from Coal Age rocks of Illinois. Nearly all came from the Mazon Creek-Braidwood area in Will and Grundy Counties where they are found preserved in ironstone nodules along with well-known plant fossils. Even through a fairly large number of fossil insects have been collected, it is necessary to examine thousands of concretions in order to have a chance of finding a single specimen.

Most of the fossils have no modern counterparts, but such familiar things as dragonflies, damselflies, and cockroaches are found. Many were giants of their race. The insects were of the kind that would be expected in a swamp growing near a low-lying seashore, and they probably lived among the plants that furnished woody material for the coal beds that were formerly mined.

images of conodont fossils