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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 Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
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 Species Epeorus grandis

Where & when

Time of year : June through early August

Preferred waters: Small streams

Altitude: Above 5,000 feet

In 9 records from GBIF, adults of this species have been collected during July (33%), May (22%), June (22%), August (11%), and April (11%).

In 7 records from GBIF, this species has been collected at elevations ranging from 131 to 8500 ft, with an average (median) of 3363 ft.

Species Range

Nymph biology

Current speed: Fast

Environmental tolerance: Requires very cold streams

Specimens of the Mayfly Species Epeorus grandis

3 Nymphs

Start a Discussion of Epeorus grandis

References

Mayfly Species Epeorus grandis

Species Range
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