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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.

Lateral view of a Onocosmoecus (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.
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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Female Ephemerella excrucians (Pale Morning Dun) Mayfly Dun Pictures

This "specimen" is actually two different duns, one missing the middle front and back left legs, the other missing the terminal filament i.e. middle tail. I added them together by accident, but since they're the same species, stage, and gender, I might as well leave them together.

Ruler view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho The smallest ruler marks are 1 mm.
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Lateral view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Dorsal view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Ventral view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho
Ruler view of a Female Ephemerella excrucians (Ephemerellidae) (Pale Morning Dun) Mayfly Dun from the Big Lost River in Idaho The smallest ruler marks are 1 mm.

This mayfly was collected from the Big Lost River in Idaho on August 2nd, 2020 and added to Troutnut.com by Troutnut on August 18th, 2020.


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Female Ephemerella excrucians (Pale Morning Dun) Mayfly Dun Pictures

Collection details
Location: Big Lost River, Idaho
Date: August 2nd, 2020
Added to site: August 18th, 2020
Author: Troutnut
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