Male Epeorus frisoni Mayfly Dun Pictures

This Epeorus species was the only significant hatch I encountered in the remote headwaters of a Catskill stream one afternoon (September 6th, 2006). The small stream is incredibly clear and reportedly very acidic. The duns were coming off sporadically all afternoon and evening on this pleasantly warm, mostly cloudy day with a fleeting dash of rain at one point and sunshine at another. The female spinners were around the whole time but were much more common over the riffles toward evening in groups of 2-10. They were diving to the surface to lay eggs by quickly dipping their abdomens into the water and rising up again for a repeated run.

I couldn't find any male spinners, which might make identification impossible, but I did photograph the following:

• This intact male dun.


• A female spinner


• A female dun


• A larger, damaged male dun

Hopefully this will be enough to eventually puzzle out the ID of this pretty little species.

Nice photos, Jason. Are these the fall Sulphur Mayflies that have been discussed here and on a Pennsylvania web site?