Any of numerous weak-flying insects of the order Plecoptera, whose flat, elongated nymphs live under stones along the banks of streams. After hatching from the egg, the stonefly nymphs may remain dormant for several months during late spring and summer after which they pass through several molts before becoming fully mature. Distinguishing characteristics of the North American stonefly nymphs include two tails, two claws on each foot, and (on many stoneflies) external gills. At full maturity, nymphs crawl from the water to a resting place. Stoneflies have fairly long antennae, and the majority of these insects are fully winged although some species have flightless, short wings, and a few are completely wingless. Most North American species are gray or brown while several forms are bright yellow and a few are green in color. Most species are active during the daytime.
