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

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

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.
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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Wiflyfisher has attached this picture to aid in identification. The message is below.
Late Season spinner (Upper Midwest)
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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?
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"Bear Swamp," PA

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

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.)
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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.

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