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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 Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
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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Male Eurylophella minimella (Chocolate Dun) Mayfly Spinner Pictures

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.

Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Lateral view of a Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Dorsal view of a Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Ventral view of a Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin
Male Eurylophella minimella (Ephemerellidae) (Chocolate Dun) Mayfly Spinner from the Teal River in Wisconsin

This mayfly was collected from the Teal River in Wisconsin on June 4th, 2005 and added to Troutnut.com by Troutnut on May 24th, 2006.

Discussions of this Spinner

Thoughts
5 replies
Posted by Taxon on Jul 10, 2006
Last reply on Mar 7, 2013 by Entoman
Jason-

Your identification appears spot on. You may well have already considered them, but here are three key matches:

1} Genitalia illustrated in Leonard & Leonard p. 125 figure 75, which seems to match the claspers perfectly, and would likely match the penes perfectly as well, were they not a bit damaged
2) Sternites "with four small dots sometimes elongaged into narrow streaks" as described in Leonard & Leonard p. 50
3) "stigmatic area of fore wing milky" as described in Leonard & Leonard p. 50
Thoughts on this identification?
Posted by Troutnut on Jul 10, 2006
Last reply on Jul 10, 2006 by Troutnut
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.

Start a Discussion of Spinner

References

  • Allen, R.K., and Edmunds, George F. Jr. 1963. A Revision of the Genus Ephemerella (Ephemeroptera: Ephemerellidae) VII. The Subgenus Eurylophella. Canadian Entomologist 95: 597-623.

Male Eurylophella minimella (Chocolate Dun) Mayfly Spinner Pictures

Collection details
Location: Teal River, Wisconsin
Date: June 4th, 2005
Added to site: May 24th, 2006
Author: Troutnut
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