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.

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Neoleptophlebia Mayfly Nymph Neoleptophlebia Mayfly Nymph

Dorsal view of a Neoleptophlebia (Leptophlebiidae) Mayfly Nymph from the Yakima River in Washington

Some characteristics from the microscope images for the tentative species id: The postero-lateral projections are found only on segment 9, not segment 8. Based on the key in Jacobus et al. (2014), it appears to key to Neoleptophlebia adoptiva or Neoleptophlebia heteronea, same as this specimen with pretty different abdominal markings. However, distinguishing between those calls for comparing the lengths of the second and third segment of the labial palp, and this one (like the other one) only seems to have two segments. So I'm stuck on them both. It's likely that the fact that they're immature nymphs stymies identification in some important way.

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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

Jacobus, L. M., Wiersema, N.A., and Webb, J.M. 2014. Identification of Far Northern and Western North American Mayfly Larvae (Insecta: Ephemeroptera), North of Mexico; Version 2. Joint Aquatic Science meeting, Portland, OR. Unpublished workshop manual. 1-176.
Zloty, J and Pritchard, G. 1997. Larvae and adults of Ameletus mayflies (Ephemeroptera: Ameletidae) from Alberta. Canadian Entomologist 129: 251-289.