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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.
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.

Caddisfly Genus Psilotreta (Dark Blue Sedges)

It pays to learn the quirks of this very abundant and unusual genus. Its hatches stumped Gary LaFontaine for years before he learned their subtleties, prompting him to give the most common species, Psilotreta labida, the nickname "Slap-in-the-Face Caddis."

Where & when

Time of year : Mid-June to late July

The most important species are found in the East. They often emerge together with the large Green Drake mayflies, Ephemera guttulata, which can be reduced to a masking hatch when these caddisflies are thick.

In 52 records from GBIF, adults of this genus have mostly been collected during June (60%), May (33%), and July (6%).

In 33 records from GBIF, this genus has been collected at elevations ranging from 20 to 5614 ft, with an average (median) of 2356 ft.

Genus Range

Hatching behavior

Time of day : Evening

Because the larvae gather in large numbers on certain rocks to pupate, fishing the emergence demands unusual tactics from the angler. Gary LaFontaine describes them in Caddisflies:

A hundred or more cases might be stacked in layers on the underside of a particular rock. When the emergence period begins the pupae pop continually from this area. They escape from the cocoon and wash out from under the rock, creating a food line for trout on the downstream side of the pupation site. During the peak evening hours the emerging pupae may create feeding situations in only a small part of the stream. They attract trout into these prime zones (which fly fishermen can find beforehand by searching for the clusters of pupae).

Egg-Laying behavior

Time of day: Evening

The females flop onto the surface and flitter around in a non-stop commotion there until they're through laying their eggs. Trout key on the fluttering insects and reportedly reject still imitations.

Larva & pupa biology

Diet: Omnivorous

Substrate: Silt, sand, or gravel

Environmental tolerance: Prefers cool streams

Shelter type: Horn-shaped sand and gravel cases

These are burrowing caddisflies, and their cases are extremely strong. They live in the silt, sand, or gravel for most of their lives, where they are not vulnerable to trout. They expose themselves only when they are ready to pupate, when they congregate on specific rocks.

Specimens of the Caddisfly Genus Psilotreta

1 Male Adult
1 Larva

Start a Discussion of Psilotreta


Caddisfly Genus Psilotreta (Dark Blue Sedges)

Species in Psilotreta: Psilotreta frontalis, Psilotreta labida
4 species (Psilotreta amerus, Psilotreta indecisa, Psilotreta rossi, and Psilotreta rufa) aren't included.
Genus Range
Common Name
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