Stonefly Larvae

There are hundreds of species in North America
Family

There are several North American families in the order Plecoptera (stoneflies)

Description

Stonefly 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 on the head 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.

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.

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.

Key Identifiers
  • Aquatic, flattened.
  • Legs 6, sprawling, joined to middle part of body
  • Abdomen segmented.
  • The 2 antennae are long (2, 3, or more times as long as the head).
  • Tip of abdomen has 2 long threadlike “tails” (cerci).
  • Gills are tuftlike and positioned at the bases of the legs.
  • No gills (feathery structures) on the rear half of the body.
  • Each foot has 2 claws.
  • Usually found in cool, clear streams.
Size

Larva length: ½ to 1½ inches (varies with species; does not include appendages).

Habitat and conservation

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.

Foods

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.

Distribution in Missouri

Statewide.

Status

Nine Missouri stoneflies are Species of Conservation Concern and thus are vulnerable to becoming extirpated from our state. A “stonefly” is any insect in the order Plecoptera. An order is a category larger than a family. There are more than 3,000 species of stoneflies worldwide, and more than 650 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’ only function is to reproduce. Egg masses are usually deposited on the water’s surface. The adults die soon after reproducing.

Human connections

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.

Ecosystem connections

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.