Header image
Enter a name
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.

Lateral view of a Psychodidae True Fly Larva from Mystery Creek #308 in Washington
This wild-looking little thing completely puzzled me. At first I was thinking beetle or month larva, until I got a look at the pictures on the computer screen. I made a couple of incorrect guesses before entomologist Greg Courtney pointed me in the right direction with Psychodidae. He suggested a possible genus of Thornburghiella, but could not rule out some other members of the tribe Pericomini.
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.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Male Ecdyonurus criddlei (Little Slate-Winged Dun) Mayfly Spinner Pictures

This one was very puzzling to identify. It's clearly Heptageniidae. It keys pretty easily to couplet 58 in Merritt, Cummins, & Berg 5th Edition, but that's where things get tricky.

58: Male penes distinctly L-shaped; Segment 1 of foretarsi usually 1/3 to 2/3 the length of segment 2
58': Males penes not distinctly L-shaped; Segment 1 of foretarsi usually 1/5 to 1/2 the length of segment 2

The characteristics conflict here, as I'd say the penes ARE L-shaped, but the fore tarsal ratio is less than 1/3. Maybe the weasel word "usually" allows for that, and it's some kind of Stenonema, for which I'm not aware of any records in Montana, let alone western Montana.

Going by the tarsal ratio and assuming it's not Stenonema, everything in couplet 60 points to Afghanurus: contiguous compound eyes, genitalia similar to fig 13.222 in MC&B, and weakly developed basal costal crossveins in the forewings. But I looked up the original descriptions of the three Afghanurus species, and the body sizes (flowersi 5-7 mm, inconspicua 4 mm, joernensis 6-7 mm) are way below this one's 10 mm.

This led me to notice that the closely related Ecdyonurus is not included in the key at all, so I checked the descriptions of those species and found that Ecdyonurus criddlei fits very well: the color of the legs, the markings on the tergites and sternites, the short fore tarsus and ratios of the segments, etc. It was originally described as 7 mm, smaller than the 10 mm body of this specimen, but synonyms have been described with larger sizes including wing lengths up to 11 mm for females for Heptagenia salvini.

This specimen was found with a female nearby, which I think is probably the same species, although it is difficult to be certain.

Ruler view of a Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana The smallest ruler marks are 1 mm.
Lateral view of a Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Dorsal view of a Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Ventral view of a Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana
Male Ecdyonurus criddlei (Heptageniidae) (Little Slate-Winged Dun) Mayfly Spinner from the Bitterroot River in Montana

This mayfly was collected from the Bitterroot River in Montana on September 6th, 2021 and added to Troutnut.com by Troutnut on September 8th, 2021.


Start a Discussion of Spinner

Male Ecdyonurus criddlei (Little Slate-Winged Dun) Mayfly Spinner Pictures

Collection details
Location: Bitterroot River, Montana
Date: September 6th, 2021
Added to site: September 8th, 2021
Author: Troutnut
Troutnut.com is copyright © 2004-2024 (email Jason). privacy policy