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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.

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 Glossosoma (Little Brown Short-horned Sedges)

The sporadic emergence of these caddisflies diminishes the importance of the freshly emerged adults and pupae, but they have unique periods of vulnerability as larvae during the day and again as diving egg layers at dusk that can make them very important. A taxon can only have one common name attached in the title but this is one of those genera whose species come in a variety of colors and descriptive common names. In the West their bodies generally come in tan to brown shades with matching wings, their wings can be speckled grayish tan or even almost black as with an eastern species. Some western rivers have astounding populations. See Glossosomatidae for more information.

Where & when

Time of year : Early Summer

Preferred waters: Riffle sections

In 313 records from GBIF, adults of this genus have mostly been collected during July (28%), June (25%), April (12%), August (11%), May (11%), and September (7%).

In 123 records from GBIF, this genus has been collected at elevations ranging from 3 to 9239 ft, with an average (median) of 699 ft.

Genus Range

Hatching behavior

Time of day : variable and sporadic

The pupae emerge on the surface, or by rising to the surface and then swimming to shore. The generally tend to trickle off all day in numbers too few to attract much interest or notice from either angler or trout.

Egg-Laying behavior

Time of day: evenings, often at last light

Females dive underwater to oviposit. They can swarm in tremendous numbers, often mixed with several species.

Larva & pupa biology

Current speed: Fast, for most species

Shelter type: Rocks, shaped kind of like a turtle shell

Because Glossosoma cases are built to a fixed size, the larvae have to abandon them and build new ones as they grow. In the process they often accidentally or deliberately end up drifting downstream for awhile. They synchronize this activity as tightly as most species synchronize emergence, prompting trout to feed selectively on the larvae. Even better news for the angler is this activity is diurnal. Unfortunately, the timing is not predictable and while generally a morning occurrence, it can happen any time of day. A further handicap is that the behavioral drift is not visible. The angler will only know it's happening by periodically seining the drift or fishing proper imitations until the fish start to respond.

This usually occurs several times during their development in the spring and summer. In Caddisflies, LaFontaine recommends imitating the naked pinkish-colored larvae drifting without their cases. They also come in shades of pale tan or yellow.

Specimens of the Caddisfly Genus Glossosoma

1 Adult
2 Male Adults
1 Larva

2 Underwater Pictures of Glossosoma Caddisflies:

Discussions of Glossosoma

Glossosoma intermedium or nigrior
5 replies
Posted by Wiflyfisher on Jun 30, 2020
Last reply on Jul 31, 2020 by Creno
Caught and photographed in the Upper Midwest on May 12, 2020. I resized my original photo for the website.

pupa color
7 replies
Posted by LittleJ on Apr 19, 2008
Last reply on Apr 22, 2008 by LittleJ
I was thinking very dark olive w/a ginger shuck. Sound right to any of you?

Start a Discussion of Glossosoma


Caddisfly Genus Glossosoma (Little Brown Short-horned Sedges)

13 species (Glossosoma bruna, Glossosoma excita, Glossosoma idaho, Glossosoma mereca, Glossosoma oregonense, Glossosoma parvula, Glossosoma pterna, Glossosoma pyroxum, Glossosoma schuhi, Glossosoma sequoia, Glossosoma ventralis, Glossosoma verdona, and Glossosoma wenatchee) aren't included.
Genus Range
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