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> > Distance between the eyes of male Epeorus

This topic is about the Mayfly Genus Epeorus

There is remarkable variety of form and color within this prolific genus of fast-water mayflies. Different species are found across the country, and several cause good hatches. Fly anglers are likely to encounter the lesser species on occasion, too.

The best Epeorus hatch in the East is Epeorus pleuralis, the famous Quill Gordon, the first abundant large mayfly hatch of the year. Epeorus vitreus comes a little later and is important in both the East and Midwest.

In the West, Epeorus longimanus dominates in fast, high-altitude streams, while Epeorus albertae inhabits slower and lower waters. Read more...

There are 44 more specimens...

The Discussion

TroutnutMay 3rd, 2007, 10:39 am
Administrator
Bellevue, WA

Posts: 2533
There has been some discussion here before about Epeorus identification, especially the distance between the eyes of the adult males, which is one identifying characteristic. The keys say that the distance should be "less than the width of the median ocellus," but I have collected a few male duns that didn't quite fit that requirement.

We figured they were Epeorus anyway, so it's not a big deal, but a new specimen I collected sheds a bit of light on the question.

I collected a dun whose eyes were also a bit far apart, which you can see here:

http://www.troutnut.com/specimen/681

Then it molted into a spinner:

http://www.troutnut.com/specimen/682

The spinner's eyes were really almost touching, well within the description of the genus. So that answers our question: the duns may have a little wider spread and the gap will close up in the spinners.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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