StoneFly Entomology

Posted in Entomology.

This page will help you learn to identify Stoneflies so when you encounter them you will be able to identify the insect and then match the hatch  with the proper fly. Check out Jason Neuswanger aquatic insect site from Cornell University on Aquatic Insect guide to Entomology for Trout Fishing

The Order Plecoptera, known as the Stone fly.  The stoneflies are terrestrial as adults, but in the nymphal stages they are strictly aquatic, and most are restricted to flowing waters of relatively high oxygen concentrations due to their gills. That is why they are usually found in faster moving water.

Fertile eggs are laid over or in the water and requite two to three weeks for hatching in many species, and several months among some larger forms. The nymphal instars, from 10 to over 30 moltings, occur in one to three years. Adults live from 1 to 4 weeks. Most adults are winged, although a few species are wingless or have short wings. The adults do not fly well and this has prevented them from crossing even small geographical barriers.

Temperate species that over winter as nymphs often do not stop growing even in water temperatures close to 0°C. It seems that it is warm water temperatures rather than cold ones that punctuate stonefly life cycles. The ability to spend the summer in stasis enables some species to live in temporary streams.

Generally, stonefly nymphs are either shredders or predators. Some groups that are predaceous as late instars have been reported to be herbivorous or detritivorous in early instars, while late instars of large detritivores may consume some prey. Predators are engulfers, that is, they swallow their prey whole or bite off and swallow parts of prey. They are active search or pursuit predators, using their long filamentous antennae to locate prey using tactile, wave disturbance, and chemical cues. Many species are opportunistic feeders, consuming prey in proportion to their relative abundance. Other species are selective for prey species or sizes. In some families adults feed, and in others they do not.
Most species appear to emerge at night and generally the males start to emerge before the females though there is considerable overlap. It is thought that both temperature and photoperiod are important in determining emergence times

After emerging the adults fly, or in the case of the flightless species crawl up into the trees. Flightlessness occurs in a number of species, sometimes only in the males sometimes in both species, occasionally it is accompanied by winglessness. In some species the adults feed and in others they don't. The non-feeding species tend to emerge with fully formed eggs, to mate quickly and to lay their eggs and die after only a few days. Males tend to live only a few days in most species anyway, however the females in feeding species may live for 4 to 5 weeks

Males drum (beat their abdomen on the substrate i.e. what ever they are standing on) to attract females, and females drum in reply, the frequencies are species specific and are transmitted through the substrate not through the air. The normal sequence is 1) male drums, 2) female drums back, 3) male moves a little way towards female and drums again, 4) female drums back again, 5) male moves closer to female and drums some more, 6) female drums back again, eventually after an indefinite amount of communication the pair meet and mate. Females only mate once and mated females do not reply to males