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.

A trackless paradise two days deep in the Yellowstone backcountry

From Mystery Creek # 218 in Wyoming

Stream photos

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Perlodidae (Springflies and Yellow Stones) Stonefly Nymph Perlodidae (Springflies and Yellow Stones) Stonefly Nymph

Artistic view of a Perlodidae (Springflies and Yellow Stones) Stonefly Nymph from the Yakima River in Washington

This one seems to lead to Couplet 35 of the Key to Genera of Perlodidae Nymphs and the genus Isoperla, but I'm skeptical that's correct based on the general look. I need to get it under the microscope to review several choices in the key, and it'll probably end up a different Perlodidae.

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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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Ameletus velox (Brown Dun) Mayfly Nymph Pictures

This Ameletus has puzzled me since I found their exuviae four years ago. Using the key in Larvae and adults of Ameletus mayflies (Ephemeroptera: Ameletidae) from Alberta this appears to key to Ameletus velox. It also sort of matches the color pattern on abdominal segments 6-7 from their figure 20C, which their text mentions as another identifying characteristic. However, one characteristic ("incisor area of left mandible with second denticle much smaller than first") doesn't seem to match. Also, velox is reportedly among the largest Ameletus species, but not quite as large as this nymph. My best guess is still that it represents a bit of undocumented variation on velox.

Lateral view of a Ameletus velox (Ameletidae) (Brown Dun) Mayfly Nymph from Mystery Creek #199 in Washington

Dorsal view of a Ameletus velox (Ameletidae) (Brown Dun) Mayfly Nymph from Mystery Creek #199 in Washington

Ventral view of a Ameletus velox (Ameletidae) (Brown Dun) Mayfly Nymph from Mystery Creek #199 in Washington

Ameletus velox (Ameletidae) (Brown Dun) Mayfly Nymph from Mystery Creek #199 in Washington

Ruler view of a Ameletus velox (Ameletidae) (Brown Dun) Mayfly Nymph from Mystery Creek #199 in Washington The smallest ruler marks are 1 mm.

This mayfly was collected from Mystery Creek #199 in Washington on June 19th, 2023 and added to Troutnut.com by Troutnut on June 21st, 2023.

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References

Zloty, J and Pritchard, G. 1997. Larvae and adults of Ameletus mayflies (Ephemeroptera: Ameletidae) from Alberta. Canadian Entomologist 129: 251-289.