stonefly

stonefly, any insect of the order Plecoptera. North American species, of which there are more than 200, are yellowish, greenish, or brownish in the adult stage and have transparent wings, usually two pairs, but seldom fly. The eggs are deposited in the water; the abundant aquatic nymphs are found under stones, hence their name. Since the gills are poorly developed, the nymphs are confined to well-aerated waters, such as fast streams, where they form one of the most important food supplies for fresh-water fishes. One to three years may be required to reach the adult stage. Fishermen refer to adult stoneflies as browns and imitate their shape in lures. Stoneflies are classified in the phylum Arthropoda, class Insecta, order Plecoptera.

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stonefly

Stonefly (Plecoptera)

(credit: William E. Ferguson)

Any of some 1,550 insect species (order Plecoptera) with adults, about 0.25–2.5 in. (6–60 mm) long, that are generally gray, black, or brown. They have long antennae; weak, chewing mouthparts; and two pairs of membranous wings that, at rest, fold like a fan. The hind wings are generally broader but shorter than the forewings. Despite their well-developed wings, stoneflies are poor fliers. The female drops a mass of up to 6,000 eggs into a stream. Nymphs resemble adults but are wingless and may have external gills; they feed on plants, decaying organic matter, and insects. The nymphal stage lasts one to four years; adults live several weeks.