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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Kogotus (Perlodidae) Stonefly Nymph from Mystery Creek #199 in Washington
This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
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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Ephemerella aurivillii Mayfly Nymph Pictures

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.

Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Dorsal view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ventral view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington
Ruler view of a Ephemerella aurivillii (Ephemerellidae) Mayfly Nymph from the Foss River in Washington The smallest ruler marks are 1 mm.

This mayfly was collected from the Foss River in Washington on September 10th, 2020 and added to Troutnut.com by Troutnut on September 19th, 2020.

Discussions of this Nymph

Ephemerella nymph
Posted by Millcreek on Sep 24, 2020
Last reply on Sep 24, 2020 by Millcreek
Jason,
I think this nymph may be Ephemerella tibialis. I am basing this on the following papers by Allen and Edmunds.

http://www.ephemeroptera-galactica.com/pubs/pub_a/puballenr1963p583.pdf

http://www.ephemeroptera-galactica.com/pubs/pub_a/puballenr1965p244.pdf

Ephemerella tibialis is in the paper on Serratella.

Start a Discussion of Nymph

Ephemerella aurivillii Mayfly Nymph Pictures

Collection details
Location: Foss River, Washington
Date: September 10th, 2020
Added to site: September 19th, 2020
Author: Troutnut
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