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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 Skwala (Perlodidae) (Large Springfly) Stonefly Nymph from the Yakima River in Washington
This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.
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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Male Ameletus vernalis (Brown Dun) Mayfly Nymph Pictures

Keying this one out using Zloty & Pritchard 1997:
-No ganglionic markings on sternites 2–8
-Posterior margins of sternits 6–8 without numerous spines
-Mesal gill extension well developed (I really don't like the "well developed" language when it's subjective, but in this case the other option doesn't lead anywhere productive)
-Tails pale in basal 1/3
-Larger species (13–16 mm) — this one is just shy of 12 mm, but closer to 13 than to <10
-Spring emergence
This all points to Ameletus vernalis.

Ruler view of a Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington The smallest ruler marks are 1 mm.
Dorsal view of a Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington
Ventral view of a Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington
Lateral view of a Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington
Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington
Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington
Closeup of one of the middle gills under the microscope.

Male Ameletus vernalis (Ameletidae) (Brown Dun) Mayfly Nymph from the Icicle River in Washington

This mayfly was collected from the Icicle River in Washington on June 3rd, 2022 and added to Troutnut.com by Troutnut on June 4th, 2022.


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Male Ameletus vernalis (Brown Dun) Mayfly Nymph Pictures

Collection details
Location: Icicle River, Washington
Date: June 3rd, 2022
Added to site: June 4th, 2022
Author: Troutnut
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