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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.

Mayfly Species Epeorus vitreus (Sulphur)

This is the second most common Epeorus species in the East and Midwest. Most anglers will encounter sporadic hatches of Epeorus vitreus once in a while, and sometimes a more concentrated emergence causes a good rise of fish.

Where & when

Time of year : Mid-May through early September, peaking in May-June

This Midwestern hatch of Epeorus vitreus is a week or two behind the Eastern emergence.

I believe I encountered a fishable hatch of this species in the Catskills in early September, but I could not positively identify the flies.

Hatching behavior

Time of day : Late afternoon and evening, peaking at dusk

Epeorus vitreus emerges underwater. The duns reportedly leave their nymphal shucks while rising to the surface rather than on the bottom.

Spinner behavior

Time of day: Early evening; later on hot days

Habitat: Riffles

The females oviposit by flying low over the water and repeatedly dipping their abdomens in and out. When they're done, they fall spent with the males.

Nymph biology

Current speed: Medium to fast

Substrate: Boulders and gravel

These mayflies survive under a wider range of conditions than Epeorus pleuralis, but they do require a rock or gravel bottom. They do best in fast water.

Epeorus vitreus Fly Fishing Tips

At a distance, this species is easily mistaken for other Sulphur species like Ephemerella invaria by the untrained eye who does not look beyond size and color. This is one more reason to quickly collect a dun if you're having trouble matching a Sulphur hatch.

Specimens of the Mayfly Species Epeorus vitreus

4 Female Spinners
1 Male Spinner
2 Female Duns
1 Male Dun
Male Epeorus vitreus (Sulphur) Mayfly Dun
This is my favorite mayfly from 2004, and it appears on my popular Be the Trout: Eat Mayflies products. Check them out!

Its identification is really up in the air. It might be a late-season vitreus dun but it may very well be one of the more obscure species in that genus.
7 Nymphs

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References

Species Range
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