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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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Isoperla fusca (Yellow Sally) Stonefly Nymph Pictures

This specimen keys to Isoperla fusca using the key in Szczytko & Stewart 1979, but some species of Isoperla weren't represented there. It's probably the same species as this one collected a year later. Despite taking many good pictures of both, I'm not sure of the species ID.

Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Dorsal view of a Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Ruler view of a Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington The smallest ruler marks are 1 mm.
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
The row of stout setae along the back of the head (anterior of the occiput) on this specimen was relevant to the species ID.

Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington
Isoperla fusca (Perlodidae) (Yellow Sally) Stonefly Nymph from the Yakima River in Washington

This stonefly was collected from the Yakima River in Washington on April 9th, 2021 and added to Troutnut.com by Troutnut on April 12th, 2021.


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Isoperla fusca (Yellow Sally) Stonefly Nymph Pictures

Collection details
Location: Yakima River, Washington
Date: April 9th, 2021
Added to site: April 12th, 2021
Author: Troutnut
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