Stoneflies

Media
Photo of an adult stonefly on a leaf
Scientific Name
Nearly 700 species in North America north of Mexico
Family
About 9 North American families in order Plecoptera (stoneflies)
Description

Adults have two pairs of wings that are clear, membranous, and finely veined and rest closely down the back of the body, the forewings covering the hindwings. Antennae are threadlike and long. Colors are usually dull, dark, and drab brown, yellow, or sometimes green.

Larvae (also called nymphs or naiads) are aquatic, flattened, with 6 sprawling legs and with a segmented abdomen bearing 2 long antenna-like “tails” (cerci). The antennae are long, too. Gills are tuftlike and usually positioned at the bases of the legs, on the underside of the body. Each foot has 2 claws.

To identify the many different kinds of stoneflies, one must use a magnifying lens and note details of mouthparts, wing vein patterns, leg segments, cerci, gills, and more.

Common Name Synonyms
Plecopterans
Size
Body length: usually ranges from ½ to 2 inches (varies with species).
Where To Find
image of Stoneflies Distribution Map
Statewide.
There are many types of stoneflies, which naturally live in different habitats. As nymphs, most inhabit clean, flowing streams, rivers, and springs, where the current is brisk. They usually creep under rocks and other submerged objects. Some species prefer lakes, ponds, and other quiet waters. Adults are poor fliers and usually stay close to water and in shady areas, such as the undersides of leaves or under bridges. Some species are nocturnal; many are attracted to artificial lights.
The food habits of the different species vary. Nymphs typically have mouthparts adapted for chewing, and many eat plant material. Others nymphs are carnivorous, eating smaller aquatic invertebrates. Many species of stoneflies lose the ability to eat when they undergo their final molt and become adults. Some species retain functioning mouthparts, however, and do eat as adults. Many of these eat algae or other plant material.

Nine Missouri stoneflies are Species of Conservation Concern and thus are vulnerable to becoming extirpated from our state.

Technically, a stonefly is any insect in the order Plecoptera. An order is a category larger than a family. There are nearly 3,500 species of stoneflies worldwide, and more than 670 in North America. Describing the characteristics of stoneflies is like describing all the beetles.

Life Cycle
Depending on the species, stoneflies may live for 1 or 2 years underwater in the immature, larval form. When growth is complete, usually in the summer, the nymph crawls out of the water (often onto stones, hence the name), molts, and emerges as a winged adult. At this point, the mouthparts of many species are nonfunctioning, as the adults’ function is only to reproduce. Egg masses are usually deposited on the water’s surface. The adults die soon after reproducing.
Most people are completely unaware that stoneflies exist, unless they happen to witness a large group of adult stoneflies congregating, usually near a stream. Many fly fishers, however, consider imitation stoneflies the lure of choice for trout and salmon.
Stonefly larvae are a favorite food of many types of fish. Also, because they require clean, well-oxygenated water, their presence is a sign of good water quality. When stoneflies disappear from a stream where they used to live, it is a sign that something is wrong with the water.
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About Land Invertebrates in Missouri
Invertebrates are animals without backbones, including earthworms, slugs, snails, and arthropods. Arthropods—invertebrates with “jointed legs” — are a group of invertebrates that includes crayfish, shrimp, millipedes, centipedes, mites, spiders, and insects. There may be as many as 10 million species of insects alive on earth today, and they probably constitute more than 90 percent all animal species.