This dun molted most of the way into a spinner (though the wings got stuck) the evening after I photographed it, so I took some more photos of the spinner.
I found a female nearby, probably of the same species.
Entoman on Oct 25, 2011October 25th, 2011, 11:39 am EDT
Hi Jason,
Excepting Bob Newell's nymphs, I believe the photos on the Acerpenna genus hatch page are actually Baetis. Looking closely at the images shows characters hard to reconcile with Merritt IV couplet 37(36') for Acerpenna that reads in part as follows, "...beyond costal process anterior margin of hind wing undulate; terminal segment of male forceps approximately four times as long as wide..."
The specimens do match up with Baetis by the process of elimination as the preceding couplets and those that follow rule out other possibilities by negative determination. The characters of baetis are so variable that the keys have to be structured this way, I guess.
Regards,
Kurt
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman