Stoneflies, Order Plecoptera

Aquatic stonefly nymphs live only in cool, clean streams, and are an important bioindicator of good water quality. Stoneflies belong to the order Plecoptera, which comes from the Greek for "twisted wings."

Description

Adult stoneflies are fairly drab insects, with flattened, soft bodies. They hold their wings flat over the bodies when at rest. Stonefly adults have long, threadlike antennae, and a pair of cerci extends from the abdomen. Stoneflies have two compound eyes and three simple eyes and chewing mouthparts, though not all species feed as adults.

Stoneflies fly poorly, so they don't stray far from the stream where they lived as nymphs. Adults are short-lived. Stoneflies exhibit unusual courtship behavior. The males drum their abdomens on a substrate to send an acoustic signal to potential female mates. A receptive female drums her response. The pair will continue to drum to each other, gradually moving closer and closer until they meet, and mate.

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After mating, females deposit their eggs in the water. Stonefly nymphs develop slowly, taking 1 to 3 years to molt repeatedly before emerging as adults. Stoneflies are so named because the nymphs often live under stones in streams or rivers. They feed on a variety of plant and animal matter, both dead and living, depending on the species and age of the nymph.

Habitat and Distribution

As nymphs, stoneflies inhabit cold, fast-flowing streams in pristine condition. Adult stoneflies are terrestrial but tend to stay close to the streams from which they emerge. Worldwide, entomologists identify about 2,000 stonefly species, about a third of which live in the U.S. and Canada.

Major Families in the Order

• Family Perlidae - common stoneflies
• Family Leuctridae - rolled-winged stoneflies
• Family Taeniopterygidae - winter stoneflies
• Family Nemouridae - spring stoneflies

Families and Genera of Interest

• Adult stoneflies in the subfamily Isoperlinae appear to be pollen feeders.
• Female Pteronarcys dorsata stoneflies measure as much as 55 cm in length.
• Nymphs of the family Peltoperlidae resemble cockroaches.
• The Lake Tahoe benthic stonefly, Capnia lacustra, spends its entire life cycle (even as an adult) deep within Lake Tahoe. It is an endemic species to Lake Tahoe.

Sources

• Borror and DeLong's Introduction to the Study of Insects, 7th Edition, Charles A. Triplehorn, and Norman F. Johnson.
• Order Plecoptera - Stoneflies, Bugguide.net. Accessed online February 15, 2011.
• Guide to Aquatic Insects and Crustaceans, Izaak Walton League of America.