Stoneflies: Plecoptera

In North America and Europe male and female stoneflies usually find one another by joining in mating swarms near streams and rivers. Males and females locate one another through a complex series of vibration signals known as drumming. These signals are attractive only to individuals of the same species. Stoneflies drum by tapping, rubbing, or scraping their abdomens on a rock or log. Other species produce signals by doing pushups or rocking back and forth. Males typically drum as they search for females. If interested, a female perched nearby will drum back. Both the male and female continue to communicate this way until they locate one another and mate. Males will attempt to mate many times, but females will mate only once. Mated females will not answer male drumming calls.

Males transfer sperm directly to the female's reproductive organs during mating. The eggs are laid in pellets or masses containing many eggs. The female then flies over the water, either dipping her abdomen in the water to deposit the eggs, or simply dropping them from the air. In some species the female runs along the shore to lay her eggs directly in shallow water. Other females submerge themselves completely to place their eggs directly on the stream bottom. The eggs either hatch within three to four weeks or enter diapause (DIE-uh-pawz), a period of rest that lasts three months to one or more years.

Stonefly larvae somewhat or closely resemble the adults and develop gradually. They molt, or shed their exoskeletons or hard outer coverings, ten to twenty-five times before reaching adulthood. Their life cycle may take months or years depending on species and local conditions, such as water temperature. When mature the larvae crawl out of the water and molt for the last time. Their shed exoskeletons are commonly found on rocks and vegetation near streams and rivers in spring and summer. The adults live only briefly and do not provide any care for the larvae.