Order – Plecoptera
Source of Name – “Pleco” meaning folded or plaited and “ptera” meaning wings.
There are approximately 1150 species of stoneflies in the world. Stoneflies live in cool, clean, highly oxygenated water that has a stony or rocky bottom and because of this the stonefly is a great biotic indicator of water quality. Their diet consists of small invertebrate animals, decaying plant material, organic matter, algae and bacteria. They thrive in water temperatures between 40 and 50 degrees Fahrenheit.
A stonefly prefers cold water over warm water because it holds more oxygen. One of the requirements of survival is oxygen which they take in from the water by means of external gills which are located on their head, neck, and thorax in the form of feathery white tufts. Radical increases in stream temperature or reductions in oxygen levels seriously affect a river’s stonefly population.
A stonefly does not have a pupa stage like the caddis fly, they start as eggs. During their life cycle they undergo an incomplete metamorphosis, passing through only three stages of development; egg, nymph and adult. Some species live in the water as nymphs for three years before they hatch into their adult stage. Most species of stoneflies molt 20 to 30 times in their lifetime. When they molt they turn a lighter color and have much softer shell, which makes it easier for the fish to digest and also makes them an attractive target. As their shell hardens it darkens in color.
Once a stonefly reaches its time to hatch; most species crawl to shore to shed their exoskeleton, usually in the late evening or at night. Soon after they hatch they head for the vegetation near the edge of the stream to mate and are not hard to spot due to their awkwardness in flight. Now that they are in their adult stage they have two pairs of two wings.
The males attract the females by “drumming” on their abdomen, they mate, then the female lays hundreds of eggs in slimy masses by dipping their abdomens under water or some species just drop them into the water while in flight. A female can lay between 200 and 1400 eggs. Their lifespan as an adult varies from a few days to three months depending on the species. The eggs drop into the substrate where they connect to rocks and the life cycle starts over.