Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
I have been told this is the only western aquatic moth, Petrophila confusalis, see here on milkweed blossoms.
This insect was collected from the Flathead River-lower in Montana on July 21st, 2005 and added to Troutnut.com by Bnewell on June 28th, 2011.