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.

Inlet of Upper Titcomb Lake

From Titcomb Basin in Wyoming

Stream photos

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Isoperla (Stripetails and Yellow Stones) Stonefly Adult Isoperla (Stripetails and Yellow Stones) Stonefly Adult

Dorsal view of a Isoperla (Perlodidae) (Stripetails and Yellow Stones) Stonefly Adult from Mystery Creek #308 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.

Caddis Hatches

CharlieSawd
St. Michael, Minnesota

Posts: 26

CharlieSawd on May 22, 2009May 22nd, 2009, 12:33 pm EDT

I am curious if any of you have come across any literature, or know personally why dry conditions (low precipitation and stream level) affect mayfly and caddis hatches. At first, the answer may seem intuitive, but upon further scrutiny, I am finding that is not the case.

Any help would be appreciated.
Thanks,

Charlie Sawdey
www.driftlessflybox.com

Willmilne
Manitoba Canada

Posts: 19

Willmilne on May 22, 2009May 22nd, 2009, 12:57 pm EDT

Hi

This paper dicusses diversity and densities in an unstable stream environment

http://www.famu.org/mayfly/pubs/pub_f/pubflannaganj1991p333.pdf[

and this one has some interesting data regarding flow variations and emergence densities

http://www.famu.org/mayfly/pubs/pub_f/pubflannagaj2001p97.pdf

hope that helps

Will

Konchu

Site Editor
Indiana

Posts: 498

Konchu on May 22, 2009May 22nd, 2009, 2:38 pm EDT

That IS a deceptively difficult question to answer. Here's a few thoughts and observations. No more than that.

Several local insect species develop much more quickly when the water levels drop and flow slows. One part of this is that the stream temperature increases and so does the metabolism of the bugs.

In a nearby stream that I visited about an hour ago, for example, the insects are developing pretty quickly now. We had near flood conditions about a week ago, but the stream has dried to a mere trickle this weekend. The populations of bugs are really concentrated, and I'm guessing they'll pop out any day, if they haven't already started.

I saw some fish rising and kissing the water's surface. I heard even more of this from nearby pools.