The stone fly is a curious insect that is hatched under water.  It gets its name because the nymph, or young, are generally to be found under stones in brooks or streams.

Stone Fly

When mature, the nymph crawls out of the water and shedding its skin, becomes an adult stone fly and lives among the stones and brush along the banks.

And adult stone fly may be from ½-inch to 2 inches long and is often colored to match its surroundings.

The hind pair of its four wings is so long that it is folded flat over the back when the insect is at rest.

Despite its wings, it is a poor flyer, and when disturbed it generally scuttles away rather that fly to safety.  As a result of pollution of rivers, stone flies have disappeared from many places where they were found in great numbers a few years ago.

They once formed the main diet of trout and other fishes. – Dick Rogers