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.
Adult stoneflies 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 of larvae:
- 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
Larva length: ½ to 1½ inches (varies with species; does not include appendages).
Statewide.
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.
Food
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.
Status
Ten Missouri stoneflies are species of conservation concern and thus are vulnerable to becoming extirpated from our state:
- Ozark stone, Acroneuria ozarkensis
- Pygmy snowfly, Allocapnia pygmaea
- Barbed sallfly, Alloperla hamata
- Truncate sallfly, Alloperla leonarda
- Giant stone, Attaneuria ruralis
- Austin springfly, Hydroperla fugitans
- Banded stripetail, Isoperla burksi
- Plains stripetail, Isoperla longiseta
- Spiny stone, Neoperla carlsoni
- Longhorn forestfly, Prostoia similis
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.
Technically, a stonefly is any insect in the order Plecoptera. An order is a category larger than a family. Worldwide, there are about 3,400 species of stoneflies in 18 families, and more than 670 species in 9 families in North America north of Mexico. Describing the characteristics of "stoneflies" is like describing the characteristics all the "beetles" or all the "moths."
