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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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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I wish I had photographed this one against a ruler or some kind of size reference. The genus ID is confident, and I am very tentatively calling it Eurylophella minimella based on the keys in Allen & Edmunds (1963) and the following judgment of its characteristics:
1. Has a "medium" rather than "large" tubercle on the styliger plate between the forceps bases (pretty sure)
2. Body and legs not sprinkled with fine brown dots (obvious)
3. Tails with dark annulations at the apex of each segment (obvious)
4. Terga brown and sterna pale; sterna 2-7 lacking large dark brown median macula, but each having 4 dark dots (pretty sure)
5. Penes widest near base, not mid-length (pretty sure)
6. Penes with a "shield-shaped" rather than "oblong" subapical excavation (not sure)
7. Dark brown apical macula on femora "distinct" rather than "faint" (very unsure on this judgment call)
If i'm wrong, i'm mostly likely wrong about point 7, which would make this Eurylophella verisimilis instead (forewings 8–9 mm long, vs 6–7 for minimella). If i'm wrong about point 6 (also very possible), the options would be Eurylophella aestiva and Eurylophella bicolor.
1. Has a "medium" rather than "large" tubercle on the styliger plate between the forceps bases (pretty sure)
2. Body and legs not sprinkled with fine brown dots (obvious)
3. Tails with dark annulations at the apex of each segment (obvious)
4. Terga brown and sterna pale; sterna 2-7 lacking large dark brown median macula, but each having 4 dark dots (pretty sure)
5. Penes widest near base, not mid-length (pretty sure)
6. Penes with a "shield-shaped" rather than "oblong" subapical excavation (not sure)
7. Dark brown apical macula on femora "distinct" rather than "faint" (very unsure on this judgment call)
If i'm wrong, i'm mostly likely wrong about point 7, which would make this Eurylophella verisimilis instead (forewings 8–9 mm long, vs 6–7 for minimella). If i'm wrong about point 6 (also very possible), the options would be Eurylophella aestiva and Eurylophella bicolor.
Troutnut on Jul 10, 2006July 10th, 2006, 8:27 am EDT
I've got several specimens of this small Ephemerellid species, and my best guess is Ephemerella needhami, but I'm still unsure. There are species of Eurylophella with similar stripes whose nymphs were common at the same time and in the same general location, but I didn't do really comprehensive nymph collection.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Troutnut and salmonid ecologist