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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 Sweltsa (Chloroperlidae) (Sallfly) Stonefly Nymph from the Yakima River in Washington
This species was fairly abundant in a February sample of the upper Yakima.
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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Dorsal view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
This is a puzzling one to identify and I'm not sure about the species. The maxillary palp is present and segmented, and the maxillary canines are not strongly serrate laterally. I think it's Ephemerella, not Serratella. The ventral lamellae of the gills on abdominal segment 6 have a clear median notch with a depth at least half the length of the lamellae, which points toward a couple of uncommon species (most likely Ephemerella alleni), but the abdominal tubercles and coloration don't fit that species. To add to the confusion, none of the above species are expected to emerge in the fall, as far as I know. I'm going to call this one Ephemerella aurivillii for now, but that's highly uncertain.
Healdsburg, CA

Posts: 344
Millcreek on Sep 24, 2020September 24th, 2020, 5:28 pm EDT
I think this nymph may be Ephemerella tibialis. I am basing this on the following papers by Allen and Edmunds.



Ephemerella tibialis is in the paper on Serratella.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
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Bellevue, WA

Posts: 2758
Troutnut on Sep 26, 2020September 26th, 2020, 6:53 am EDT
I was using this more recent key from Jacobus et al (not sure where to find a PDF online at the moment):

Jacobus, L. M., N. A. Wiersema and J. M. Webb. 2014. Identification of Far Northern and Western North American mayfly larvae (Insecta: Ephemeroptera), north of Mexico. Joint Aquatic Science meeting, Portland, OR. 176 pp. + suppl. Unpublished workshop manual.

Here's the relevant key couplet:

81e) Maxillary canines strongly serrate laterally; thoracic nota with small, brown excrescences (sometimes difficult to detect), especially between forewingpads = Ephemerella (Vittapallia) tibialis (very similar to E. nuda)

81e’) Maxillary canines not obviously serrate laterally; thoracic nota without small, brown excrescences = 81f

I think I did find a number of E. tibialis nymphs earlier this year in Idaho. Here's one of them. I remember being able to make out the highly serrate canines pretty clearly and possibly the excresences, and I couldn't find either one on this specimen. However, I don't have the greatest microscope and am hoping to get a better one soon, so I might take a closer look.

Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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