Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana

Salmonflies
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

The North Fork Couer d'Alene River in Idaho

Stream photos

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Female Sweltsa borealis (Boreal Sallfly) Stonefly Adult Female Sweltsa borealis (Boreal Sallfly) Stonefly Adult

Lateral view of a Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington

I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.

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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.

Which Heptageniidae species is this?

Wiflyfisher has attached this picture to aid in identification. The message is below.

Wiflyfisher

Wisconsin

Posts: 622

Wiflyfisher on Jul 12, 2008July 12th, 2008, 10:30 am EDT

I know this is probably a late season spinner, but I am not sure which Heptageniidae genus and species this would be?

John S.
https://WiFlyFisher.com

GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681

GONZO on Jul 12, 2008July 12th, 2008, 10:58 am EDT

John,

It might be Stenonema femoratum, the last remaining North American species in that genus after the others were moved into Maccaffertium. It's hard to say anything really definitive about many Light Cahill/Cream Cahill females because so many of them haven't been associated in a conclusive way. The things that suggest femoratum are the crowded cross-veins near the bulla region of the forewing and the markings on the back (tergites). Still, some of the Maccaffertium also have crowded cross-veins, and I can't see enough of the back markings to be sure they match. (In femoratum, the markings are described as a central dot with a dash on either side of it.)

Wiflyfisher

Wisconsin

Posts: 622

Wiflyfisher on Jul 14, 2008July 14th, 2008, 1:37 pm EDT

the last remaining North American species

May Stenonema remain forever in the halls of Mayfly entomology! :)

Gonzo, thanks! If I get a some free time (and I can find it) I will try to post a closer shot that I took.

John S.
https://WiFlyFisher.com