Fig. 22.—Protura. Acerentulus barberi, a proturan found on sticks and leaves in the leaf mold of forests. Actual length of adult about 0.02 inch. (Drawing from H. E. Ewing.)
Diplura
Campodeids, Japygids
Small, wingless, fragile, blind, whitish insects that run fairly rapidly. They have long antennae and either two fairly long tails or a pair of forceps-like structures at the end of the abdomen. They are terrestrial and are found chiefly under stones in humid and shady situations. [Fig. 21] shows a common campodeid, a species of Campodea, occurring commonly in Illinois.
The Diplura feed on fungi and other soil microorganisms. Although they are found most frequently under stones, they live also in the soil and in matted leaves or duff on the floor of woods. About a dozen species of Diplura occur in Illinois.
Protura
Proturans
Minute, wingless, blind insects that never grow to more than 0.05 inch long. They have no antennae and use the front legs to some extent for feeling. They are terrestrial and are found inhabiting dead twigs and leaves on the forest floor. [Fig. 22] shows Acerentulus barberi Ewing, a member of a genus which occurs in many localities in Illinois. Only a few species of proturans have been taken in the state.
Collembola
Springtails
Small, wingless insects that jump and crawl when disturbed. They have short antennae and usually a springing structure on the under side near the posterior end of the body. They live in moist places and are abundant under leaf mold and similar material. Illustrated in [fig. 23] is Achorutes armatus Nicolet, which often becomes a major pest in mushroom cellars and greenhouses.
About a hundred different species of Collembola occur in Illinois; they include some of our smallest insects. A few never grow longer than 0.007 inch; the largest approach half an inch in length. These hardy animals are active all year and are surprisingly resistant to cold. Certain species occur on snow in winter. In Illinois a small, bluish gray species, Podura aquatica Linnaeus, is found on the surface of still water at the margins of ponds and small streams.