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.

Stream photos

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Onocosmoecus (Great Late-Summer Sedge) Caddisfly Larva Onocosmoecus (Great Late-Summer Sedge) Caddisfly Larva

Lateral view of a Onocosmoecus (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Larva from the Yakima River in Washington

This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.

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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.

Stenonema vicarium (March Brown) Mayfly Nymph Pictures

I keyed this nymph to Stenonema fuscom, which is now synonymized with Maccaffertium vicarium. However, the size, markings, and time of year make me very skeptical of this identification.

Ruler view of a Stenonema vicarium (Heptageniidae) (March Brown) Mayfly Nymph from the Bois Brule River in Wisconsin

Dorsal view of a Stenonema vicarium (Heptageniidae) (March Brown) Mayfly Nymph from the Bois Brule River in Wisconsin

Ventral view of a Stenonema vicarium (Heptageniidae) (March Brown) Mayfly Nymph from the Bois Brule River in Wisconsin

This mayfly was collected from the Bois Brule River in Wisconsin on June 9th, 2005 and added to Troutnut.com by Troutnut on May 26th, 2006.

Discussions of this Nymph

M. vicarium?

8 replies

Posted by Entoman on Mar 26, 2012

Last reply on Jul 2, 2012 by Gutcutter

You were right about the markings, Jason. This is one of the paler Summer Cahill species, probably mexicanum. The inverted "U" tergal markings are very distinctive (moved to mexicanum).

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