A stonefly, (Plecoptera), adult. Photo by Drees.
Common Name: Stonefly
Scientific Name: Varies
Order: Plecoptera
Description: Adults are rather soft bodied, elongate, and have two pairs of wings which may be highly pigmented and are folded over the back when at rest. The hind wing is quite wide and is folded fan-like over the back. The head bears long slender antennae. The abdomen ends with the two “tails” (cerci). Immature stages (naiads) are elongate and flattened or cylindrical. They are 3/16 to 1 3/8 inches (5 to 35 mm) long. The head has widely separated eyes, long slender antennae and chewing mouthparts. Legs are long and end in two claws. They have gills that are finger-like or filamentous and may be branched. Gills are usually found at the base of the legs but may also be found on other parts of the head and thorax. They have two “tails.” There are only about 20 species of stoneflies known in Texas.
Life Cycle: Simple metamorphosis (incomplete). Mating takes place on the ground or on vegetation. Females may carry eggs on their abdomen before laying (ovipositing). Eggs are deposited into the water in many ways: in flight, on the waters edge or even by crawling below the surface. Naiads develop in the water and may take from three month to one year or more. They usually have twelve to twenty two stages (instars). Thereafter, they move to the edge of streams and crawl out on rocks or vegetation and molt into adults. Adults appear in winter or spring, depending on the species.
A stonefly, (Plecoptera), nymph. Photo by Drees.
Habitat, Food Source(s): Immatures (naiads) are restricted to fresh water. They are usually associated with well oxygenated streams or sections of lakes with plenty of wave action. They are predatory on a variety of other aquatic insects and invertebrates. However, some are scavengers (detritivores) which contribute to the breakdown of leaf litter and plant material in the stream. Adults can be found along the edges of streams on vegetation or attracted to lights. Adult daily (diurnal) activity patterns vary with species. Some are active at night and may be found at lights.
Adults can be found at lights or on stream side vegetation. They may only be present for a few weeks because some adults are short lived. Naiads can be found on rocks or submerged plant material in well oxygenated portions of a stream. They select a riffle area of a clear stream and pull up rocks to which they cling for inspection.
Pest Status: Uncommon and restricted to aquatic habitats; beneficial to aquatic habitats; medically harmless.
For additional information, contact your local Texas A&M AgriLife Extension Service agent or search for other state Extension offices.
Literature: McCafferty 1981.