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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Kogotus (Perlodidae) Stonefly Nymph from Mystery Creek #199 in Washington
This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
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.
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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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Stenonema vicarium (March Brown) Mayfly Nymph Pictures

Collection details
Location: Bois Brule River, Wisconsin
Date: June 9th, 2005
Added to site: May 26th, 2006
Author: Troutnut
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