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.

Waterfalls over smooth bedrock above Titcomb Lakes

From Titcomb Basin in Wyoming

Stream photos

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Limnephilus (Summer Flier Sedge) Caddisfly Larva Limnephilus (Summer Flier Sedge) Caddisfly Larva

Case view of a Limnephilus (Limnephilidae) (Summer Flier Sedge) Caddisfly Larva from the Yakima River in Washington

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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.

Insect Order Lepidoptera (Moths)

Lateral view of a Lepidoptera (Moth) Insect Adult from the Henry's Fork of the Snake River in Idaho

The order Lepidoptera includes both butterflies and moths, but moths are the most important to the angler because so many species spend part of their lives underwater. These aquatic species are similar in many ways to caddisflies.

Many species, of course, are not aquatic at all.

Hatching behavior

The pupae of aquatic moths turn into adults underwater in their cocoons, so they are not worth imitating. The emerging adults, swim away from their pupal cocoons and are vulnerable to trout until they crawl or fly away from the water.

Egg-Laying behavior

Time of day: Usually dusk or nighttime

Mirroring the behavior of caddisflies, aquatic moths may lay their eggs on the surface or dive underwater to lay them on the bottom. The diving species are the most common, and they are especially vulnerable to trout. Anglers frequently see the adults in our flashlights as we leave the stream for the night, and Swisher and Richards wrote in Selective Trout:

Because almost all of the action is at dusk and later, anglers don't realize how prolific these insects really are.

Larva & pupa biology

Diet: Algae and plankton

Shelter type: Some build silk shelters.

Aquatic moth larvae live in a variety of ways underwater, including building silken shelters. Their appearances vary tremendously in size, color, and form, but they are a rare find in most places. In all my nymph sampling I have never yet turned up an aquatic moth larva.

Specimens of Moths:

3 Adults

Lepidoptera (Moth) Insect Adult

8 Pictures

In the field, I accidentally mistook this moth for a weird-looking caddisfly. Only later did I notice the moth mouthparts and that the "hair" on the wings is actually tiny, flat scales.

Collected July 30, 2020 from the Henry's Fork of the Snake River in Idaho

Added by Troutnut on August 17, 2020

Collected July 30, 2020 from the Henry's Fork of the Snake River in Idaho and added by Troutnut on August 17, 2020

Lepidoptera (Moth) Insect Adult

5 Pictures

Collected July 30, 2020 from the Henry's Fork of the Snake River in Idaho

Added by Troutnut on August 17, 2020

Collected July 30, 2020 from the Henry's Fork of the Snake River in Idaho and added by Troutnut on August 17, 2020

Lepidoptera (Moth) Insect Adult

2 Pictures

I have been told this is the only western aquatic moth, Petrophila confusalis, see here on milkweed blossoms.

Collected July 20, 2005 from the Flathead River-lower in Montana

Added by Bnewell on June 28, 2011

Collected July 20, 2005 from the Flathead River-lower in Montana and added by Bnewell on June 28, 2011

1 Larva

Geometridae (Inchworm) Moth Larva

6 Pictures

I caught this inchworm lowering itself to the surface of a trout stream from its silk thread. I saw a couple others floating on the surface, so it's likely the trout were familiar with them.

Collected May 28, 2007 from Brodhead Creek in Pennsylvania

Added by Troutnut on June 4, 2007

Collected May 28, 2007 from Brodhead Creek in Pennsylvania and added by Troutnut on June 4, 2007

1 Streamside Picture of Moths:

View Fullsize

In this picture: Moth Family Geometridae (Inchworm).

Taken June 6, 2006

Added by Troutnut on June 30, 2006

Taken June 6, 2006 and added by Troutnut on June 30, 2006

Start a Discussion of Lepidoptera

References

LaFontaine, Gary. 1981. Caddisflies. The Lyons Press.
Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.