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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Setvena wahkeena (Perlodidae) (Wahkeena Springfly) Stonefly Nymph from Mystery Creek #199 in Washington
As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Mayfly Genus Epeorus (Little Maryatts)

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.

Where & when

In 199 records from GBIF, adults of this genus have mostly been collected during June (32%), July (24%), August (17%), May (15%), and September (7%).

In 165 records from GBIF, this genus has been collected at elevations ranging from 131 to 11145 ft, with an average (median) of 3363 ft.

Genus Range

Hatching behavior

All Epeorus duns emerge from their nymphal shucks below the surface, often while still attached to the stream bed. Most species (with the exception of Epeorus pleuralis) take to the air quickly after emerging. These two factors make wet emerger patterns especially effective during Epeorus hatches.

Spinner behavior

Female Epeorus spinners oviposit by making repeated dips to the surface. They deposit a few eggs, sometimes rest briefly, and then take off for another run.

Nymph biology

Most Epeorus species require fast, pure water flowing over gravel or boulders. Some can inhabit moderate currents.

Specimens of the Mayfly Genus Epeorus

10 Male Duns
8 Female Duns
11 Male Spinners
10 Female Spinners
19 Nymphs

3 Streamside Pictures of Epeorus Mayflies:

9 Underwater Pictures of Epeorus Mayflies:

Discussions of Epeorus

Distance between the eyes of male Epeorus
Posted by Troutnut on May 3, 2007
Last reply on May 3, 2007 by Troutnut
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.
Synonym of vitreus
3 replies
Posted by GONZO on Oct 4, 2006
Last reply on Oct 4, 2006 by Troutnut
I believe rubidus = vitreus

Start a Discussion of Epeorus

References

Mayfly Genus Epeorus (Little Maryatts)

Genus Range
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