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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.

Case view of a Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
It's only barely visible in one of my pictures, but I confirmed under the microscope that this one has a prosternal horn and the antennae are mid-way between the eyes and front of the head capsule.

I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.

The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.

Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
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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