Header image
Enter a name
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 Male Baetidae (Blue-Winged Olive) Mayfly Dun from Mystery Creek #308 in Washington
This dun emerged from a mature nymph on my desk. Unfortunately its wings didn't perfectly dry out.
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.

This topic is about the Caddisfly Genus Brachycentrus

This prolific genus includes the popular eastern early-season Apple Caddis and Grannom hatches. Their life cycles are ideal for the fly angler, and every stage is frequent trout prey.

Note that this species changes color dramatically after it emerges, and imitations of egg-laying adults should be a different color from imitations of emergers. Emergers have pale blonde, almost off-white wings and bright green bodies, while the egg-laying adults have light brownish gray wings and medium green bodies.

Example specimens

Troutnut
Troutnut's profile picture
Administrator
Bellevue, WA

Posts: 2758
Troutnut on Jun 5, 2007June 5th, 2007, 5:05 pm EDT
Check out the two streamside pictures on my Brachycentrus page. I found these clusters of dead grannoms in a few different spots along a Catskill river on May 12th, while many members of (seemingly) the same species were in the air laying eggs and occasionally falling spent and being eaten by trout.

Have you ever seen these clusters? What's the explanation?
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Taxon
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Jun 5, 2007June 5th, 2007, 7:24 pm EDT
Jason-

I would speculate that they were exclusively males, which with no further function in life, seek the company of other similarly underappreciated males, and lay back on a warm surface to expire. Can there be any other likely explanation?
Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com
Troutnut
Troutnut's profile picture
Administrator
Bellevue, WA

Posts: 2758
Troutnut on Jun 6, 2007June 6th, 2007, 3:30 am EDT
Perhaps this species swarms together on the rocks to mate, and when they're done the males stay there and die while the females fly off to lay their eggs? Seems a little more likely than "seeking company," but you're probably on to something.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Quillgordon
Schuylkill County, PA.

Posts: 109
Quillgordon on Jun 6, 2007June 6th, 2007, 4:39 am EDT

I think they were waiting for Jason to photograph them.... LOL.
Perhaps they will survive to see themselves in the next issue of
'Entomology Today'...........
Where is my fishing gear & camera ???
John...
Flyfishing is a state of mind! .............. Q.g.

C/R........barbless
GONZO
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Jun 6, 2007June 6th, 2007, 4:44 am EDT
Jason, I'd check the flow regime on the days prior to your photos. Knowing the fluctuations on that tailwater, lower release levels may simply have deposited accumulations of the dead adults in certain areas. (This might even explain why most are on their backs.)

As another take on the topic, I was reminded of LaFontaine's recounting of a Charles Wetzel observation about green sedges. Quoting Wetzel about the egg-laying habits of the females, LaFontaine writes: "Now and then the flies would congregate in a ball about one inch in diameter, rise to the surface, then float downstream, when the ball would break up." This behavior is probably unrelated to the grannom accumulations you photographed, but I thought I'd offer some alternatives to Roger's (facetious) "abandoned lover's club" explanation.
Troutnut
Troutnut's profile picture
Administrator
Bellevue, WA

Posts: 2758
Troutnut on Jun 6, 2007June 6th, 2007, 5:04 am EDT
Jason, I'd check the flow regime on the days prior to your photos. Knowing the fluctuations on that tailwater, lower release levels may simply have deposited accumulations of the dead adults in certain areas.


That would make sense; in fact, the way they're laid out, it almost seems like it has to have been done by water.

I'm doubtful that the water was high enough, though. There was slight spike the day before my visit, about 200 cfs vs 150 cfs, or a couple inches of gage height. I doubt it would have brought the water high enough to deposit the flies here, and they didn't seem to be in the most likely locations for eddies if the water was high enough. I wish now I had taken another picture from several feet back.

That may still be the explanation, but I would be more inclined to believe some behavioral alternative if one makes sense.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

Quick Reply

Related Discussions

Topic
Replies
Last Reply
6
Aug 19, 2011
by Sayfu
6
Mar 22, 2009
by DOS
0
Jul 14, 2017
by Boudy28
Troutnut.com is copyright © 2004-2024 (email Jason). privacy policy