The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
Here's a puzzling nymph. It seemed to have double-banded tibiae, although the second band wasn't very pronounced. It has quite prominent tubercles that definitely aren't black.
This mayfly was collected from unknown in Wisconsin on March 10th, 2004 and added to Troutnut.com by Troutnut on January 19th, 2006.