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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 Sweltsa (Chloroperlidae) (Sallfly) Stonefly Nymph from the Yakima River in Washington
This species was fairly abundant in a February sample of the upper Yakima.
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 Eurylophella (Chocolate Duns)

None of the species in this genus are recognized as significant hatches. Nevertheless, I have found their nymphs in my samples in many streams in both the East and Midwest.

Where & when

Time of year : May and June

This genus is widespread throughout the East and Midwest but rarely abundant. The few species for which emergence dates are available all emerge in May and June.

In 141 records from GBIF, adults of this genus have mostly been collected during June (46%), May (23%), July (20%), and April (6%).

In 44 records from GBIF, this genus has been collected at elevations ranging from 13 to 2723 ft, with an average (median) of 640 ft.

Genus Range

Nymph biology

Current speed: Slow

These nymphs probably inhabit slow water where the bottom is covered with silt or detritus. The operculate gills they possess are a common adaptation evolved by mayflies in such environments.

Specimens of the Mayfly Genus Eurylophella

3 Male Duns
2 Female Duns
4 Male Spinners
5 Female Spinners
15 Nymphs

Discussions of Eurylophella

florida mayfly nymph imitations
2 replies
Posted by Homer47 on Sep 5, 2012 in the species Eurylophella temporalis
Last reply on Sep 5, 2012 by Sayfu
Looks like an imitation would be about a #10 or #8 dark brown nymph pattern. I'm down here in north Fla and trying to match the hatch in the far north central part of the state, mostly to fool the bream. Any ideas or help would be appreciated. I found two patterns so far that seem to work- a little brown nymph with a rusty brown/orange thorax(maybe this is a good representation of the E. Temporalis), and a size 12 buzzer nymph with black body, peacock thorax and white breathing filament. The bream seemed to agree with that choice. I would like to try and copy more local insects as I figure out what they are.There are dragonflies and damselflies and mosquitoes. I could start there.

Start a Discussion of Eurylophella


  • Allen, R.K., and Edmunds, George F. Jr. 1963. A Revision of the Genus Ephemerella (Ephemeroptera: Ephemerellidae) VII. The Subgenus Eurylophella. Canadian Entomologist 95: 597-623.
  • Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
  • Knopp, Malcolm and Robert Cormier. 1997. Mayflies: An Angler's Study of Trout Water Ephemeroptera . The Lyons Press.

Mayfly Genus Eurylophella (Chocolate Duns)

Genus Range
Common Name
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