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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.

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.
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.

Female Baetis bicaudatus (BWO) Mayfly Nymph Pictures

I collected this one along with a male that was quite a bit smaller but equally ready to emerge in mid April.

I spent quite a while on the identifications, because they really don't look very much like the Baetis bicaudatus nymph I caught last year in Idaho. However, the presence of hind wing pads rules out Acentrella turbida and Iswaeon anoka, the lack of a fringe of long setae on the tibiae rules out Acentrella insignificans, range rules out Heterocloeon, and the thumb-like projection on the labial palp points to Baetis. Thus, Baetis bicaudatus is a fairly confident ID, and it's not too surprising that it looked different from my previous specimen because bicaudatus is thought to be a species complex with multiple types that haven't been fully sorted out yet.

The microscope pictures for this specimen aren't from the same exact nymph, but a mixture of a few others of the same kind that I didn't mind dissecting.

Ruler view of a Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington The smallest ruler marks are 1 mm.
Dorsal view of a Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
This one actually shows the dark-bilobed markings on the pronotum characteristic of the Baetis rhodandi group (to which Baetis tricaudatus belongs). Most specimens I've seen don't have it.

Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Dorsal view of a Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Ventral view of a Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Closeup of a tarsal claw

Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
Ventral closeup of the mouthparts highlighting the labial palps. If you view each one as an arm with a hand in a mitten, the "thumb" of the mitten is the part that points clearly toward Baetis rather than Acentrella. One of these is boxed in red.

Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
The hind wingpad is clearly visible in the bottom center but not yet darkened in this specimen.

Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington
The tibiae lack a thick fringe of setae, pointing away from Acentrella and toward Baetis instead.

Female Baetis bicaudatus (Baetidae) (BWO) Mayfly Nymph from Holder Creek in Washington

This mayfly was collected from Holder Creek in Washington on April 12th, 2021 and added to Troutnut.com by Troutnut on April 13th, 2021.


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Female Baetis bicaudatus (BWO) Mayfly Nymph Pictures

Collection details
Location: Holder Creek, Washington
Date: April 12th, 2021
Added to site: April 13th, 2021
Author: Troutnut
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