Microcoryphia
Bristletails
Wingless, somewhat cylindrical insects that run and jump with extreme rapidity. They have long antennae and three long tails. The under side of the abdomen bears several pairs of short projections called styli, which are vestiges of abdominal legs. Bristletails live in rocky places or in ground cover. A type occurring in some parts of Illinois is shown in [fig. 24]. It often occurs on rocky exposures, where it resembles the lichens and is difficult to detect.
Fig. 23.—Collembola. A, Isotoma andrei; B, Achorutes armatus; C, Neosminthurus clavatus. A and C are found in woodland leaf molds; B is frequently abundant in commercial mushroom cellars. Actual length of adults ranges from 0.03 to 0.05 inch. (Drawings A and C after Harlow B. Mills.)
Fig. 24.—Microcoryphia. A bristletail belonging to the genus Machilis, often found on lichen-covered, shaded rocks. Actual length including tail is sometimes 0.5 inch. (Drawing after R. E. Snodgrass.)
Fig. 25.—Thysanura. Thermobia domestica, a common Silverfish. Actual length about 0.3 inch.
Thysanura
Silverfish
Wingless, flat insects that run rapidly. They have long antennae and three long tails. They are terrestrial and are commonly found in dwellings. [Fig. 25] shows one of the common Silverfish, Thermobia domestica (Packard); it frequently eats book bindings and other starchy materials. Some out-of-door rare forms live in the soil and are seldom collected.