Friday, April 23, 2010

Stone Fly

I had one of the creatures pictured here land on my lap last week.  When I tried to catch it, it ran away each time, and its only attempt to fly was an awkward flight of a few inches to my other leg.  Its shape and the distinctive antenna-like cerci sticking out from behind its abdomen defined it as a stonefly.   I had seen them as larva (nymphs) when working on stream teams, but never as adults.
They are sometimes referred to as winter stone flies as the adults are usually seen between winter and June.  The escape strategy it had employed is typical of these weak fliers which would rather run,  flying only inches away when forced.  They spend much of their adult life crawling around on stones in fresh water.  The females carry hundreds or even thousands of eggs in a ball which they then deposit in the water.
The adult only lives a few weeks and many don't have a even have a digestive system.  They live as adults only long enough to breed.
The nymphs may live in the stream for 1 to 4 years, going through 11 to 30+ molts before achieving maturity and taking to land.  They require well oxygenated water to survive, so finding them in a stream assessment is a sign of good quality water.
I couldn't find any source for identifying genus and species but the Wikipedia Article is a good resource for their life cycle.  There is a lot of geographical information and references at USGS Stoneflies of the United States.  Bugguide has more than enough photographs to satisfy anyone.

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