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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.

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 Male Serratella micheneri (Ephemerellidae) (Little Dark Hendrickson) Mayfly Nymph from Mystery Creek #199 in Washington
This specimen has tarsal claws with 7 denticles and tubercles on abdominal segments 4-7 only. It keys to Serratella micheneri, as do some other specimens from the same collection that lacked the dorsal stripe.
Healdsburg, CA

Posts: 344
Millcreek on Dec 24, 2019December 24th, 2019, 2:31 pm EST
This nymph appears to be Ephemerella tibialis formerly known as Serratella tibialis. Check out Allen and Edmunds; http://www.ephemeroptera-galactica.com/pubs/pub_a/puballenr1963p583.pdf

Also check https://bugguide.net/node/view/696565/bgpage and https://bugguide.net/node/view/876178

Edit: Just noticed the other two Serratella micheneri sets of photos. These also appear to be Ephemerella tibialis.

Also spotted these two sets of photos where you identified the same or a similar nymph as Ephemerella tibialis.


"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein
Troutnut's profile picture
Bellevue, WA

Posts: 2758
Troutnut on Dec 25, 2019December 25th, 2019, 3:19 pm EST
I keyed this one under the microscope using a more recent key than Allen and Edmunds:

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 Unpublished workshop manual.

The couplet on page 64 distinguishes E. tibialis from the other species:

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)

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

If I'm remembering correctly (and I might not be), I looked pretty hard at the maxillary canines and the thoracic nota under the microscope and couldn't find the characteristics pointing to tibialis. It is a bit odd that I didn't mention that in the captions, though, so perhaps I'm misremembering or I just failed to interpret the characteristics correctly.

The key does describe Serratella as having "Abdominal terga either without tubercles or with relatively large, blunt and somewhat sinuate tubercles", and one of the other specimens I labeled as micheneri seems to have sharper tubercles than those shown in the corresponding illustration in the key.

Perhaps Luke can weigh in?
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Healdsburg, CA

Posts: 344
Millcreek on Dec 26, 2019December 26th, 2019, 3:01 am EST
Found these pictures at Bold. They're not very good quality but may give enough to identify the critters.



It would be nice to hear from Luke.
"If we knew what it was we were doing, it would not be called research, would it?"
-Albert Einstein

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