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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.

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.
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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Manitoba Canada

Posts: 19
Willmilne on May 18, 2009May 18th, 2009, 12:49 pm EDT

I have recently uncovered a locale with recorded collection records for both these species and am keen to collect and photograph specimens.Nymphs and adults . I have light traps/emergence traps for the adults but...

Does anyone have suggested substrate/stream location preferences for the nymphs? For P.vittigera all I can find is a preference for clay banks and T.primus nada.

Any help would be deeply appreciated.


Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on May 18, 2009May 18th, 2009, 5:44 pm EDT

Both species apparently burrow in clay banks. Berner (1988) offers some information. He quotes Scott et al. (1959) describing the substrate preferred by Tortopus in the Savannah River:
"The clay substrate inhabited by Tortopus is always firm, nearly always vertical, and usually exposed to swift water."
Berner notes that the burrows enter the bank at right angles forming U-shaped tubes with parallel arms. In the description of Pentagenia, he mentions this:
McCafferty (1975) collected nymphs in hard clay banks approximitely three feet below the water surface in the Wabash River in Indiana. He found the clay banks to be honeycombed by Pentagenia nymphs in the same manner that the banks of the Savannah River are honeycombed by Tortopus.
Konchu's profile picture
Site Editor

Posts: 498
Konchu on May 19, 2009May 19th, 2009, 6:07 am EDT
If you're not afraid of hard work and possibility of drowning, go for it! It takes some hard digging...
Manitoba Canada

Posts: 19
Willmilne on May 19, 2009May 19th, 2009, 11:52 am EDT
Thank you for the info. that helps a great deal as the locale offers some accessible spots that would match those descriptions.

Konchu- the work is not a problem - drowning might put a serious damper on my summer plans:)))

Manitoba Canada

Posts: 19
Willmilne on May 19, 2009May 19th, 2009, 2:55 pm EDT
Thanks for the mention of Berner and McCafferty - I found some info on the FAMU site that will be a great help.


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