Insect identification > Plecoptera > Stone flies

Stone flies

Stone fliesAdult stone flies are most numerous near streams and particularly those with a rapid current. The eggs, which are often several thousand in number, are laid in the water and the nymphs locate on the underside of stones. Some breathe through the surface of the body. Tracheal gills, when present, are not leaf-like as in the May flies but are tufts of numerous short, thread-like structures containing tracheae, a tuft or bundle just behind each leg, on the underside, and also on the first two abdominal segments. When fully grown the nymphs leave the water and molt for the last time on land.
They feed on small insects, probably largely May fly nymphs, and possibly on vegetable matter (diatoms) and are themselves a favorite food for fish.

Some species of stone flies appear in enormous numbers just as the ice is breaking up in the streams, in the Northern United States, and others are found on the snow even earlier in the season on warm days.

In general the group is without economic importance, but a few kinds of adults have recently been observed in the Northwest injuring the buds and foliage of fruit trees as these first develop, and in these species the mouth-parts are much more strongly developed than in the others. Only one thousand to fifteen hundred species are known.