Plecoptera - The Stoneflies

The stoneflies are an ancient order, evolving in the Permian period (280-225 million years ago) and perhaps sharing an ancestry with the primitive cockroaches. Today’s stoneflies differ little from their prehistoric ancestors. The word "Plecoptera" is derived from the ancient Greek words for "plait-wing", making reference to the large hind wings which are folded in plaits and lie upon the abdomen, covered by the forewings, when the insect is at rest. The common name "stonefly" comes from the flattened larvae, which are most frequently found beneath the stones of swift-flowing streams where they form an important part of the food chain. Because of their need for clean, well-oxygenated water, their presence is considered a good indicator of a stream’s health. Confined to freshwater habitats, which includes large lakes with serious wave activity, they are always found on or in the substrate. Depending on the species, larva can be carnivores, herbivores, omnivores or detrivores. This aquatic larval stage may last from 1-4 years, depending on the species. Adults live only about 2-3 weeks and eat little or nothing. The adults, usually colored some shade of brown or yellow, can most commonly be found resting on vegetation close to the body of water where they spent their “childhood”. They are weak flyers and seldom fly far from the waters from which they emerge. After mating, females disperse eggs (of which there can be up to 1000) by flying over a chosen body of water, dipping the abdomen beneath the surface of the water and ejecting eggs a few at a time. Having been around so long, some species have evolved to have the adult forms emerge and mate in winter (a tactic devised to avoid predation). The adults of these species can be found walking about on the snow that borders their streams and rivers. As long as the ambient air temperature around this water is above freezing, they are able to successfully complete their lifecycles. Because of the fact that they emerge almost year-round, many tied flies used by fly fisherman imitate them. In fact, the first artificial fly (made over 450 years ago) was based on a British stonefly. There about 3,000 known species.

169_8_thumb.jpgCommon Stone Flies (Acroneuria sp.) – adults & nymph