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3. What's happening here?

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-

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?

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.

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...

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.

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.