Plecoptera

Order

PLECOPTERA
(Greek, plekein = to fold; pteron = wing)

Description

Stoneflies are soft bodied insects that generally have two unequal pairs of membranous, intricately veined wings. However, there are some wingless species. The forewings are smaller than the hind wings and are often longer than the abdomen of the insect. Adult insects have large compound eyes with two or three simple eyes (ocelli). The antennae are long and composed of short, straight segments (filiform). The adult stage has mandibles but these are often reduced. In some species they may be functionless as the adult insect has not been observed to feed. Generally, there are two appendages at the end of the abdomen (cerci).

Life Cycle

The juveniles emerge from the eggs as miniature replicas of the adults (nymphs) but without wings. Nymphs mature through a series of moults, sometimes as many as 33. The nymphs are aquatic and possess gills as a fringe along the abdomen. The nymphs crawl about over the beds of fast flowing streams, although they can swim if necessary. Stoneflies are very quickly affected by pollution as they are unable to tolerate even minor levels of contaminants.

Food

The nymphs may feed on plants, animals and detritus, or be restricted solely to plants. Some nymphs are predators on small aquatic life. Adults feed on algae, lichens, plants or even rotten wood.

Importance

Stoneflies have no known economic importance apart from their presence in the food-chains of freshwater communities. The stoneflies may be useful components in fish food-chains.