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.
This one was collected close to a male which, based on size and general structure, was likely the same species. Females are supposed to be lighter-colored and with less distinct markings than the males, although the difference in this pair is particularly stark.
This mayfly was collected from the Bitterroot River in Montana on September 6th, 2021 and added to Troutnut.com by Troutnut on September 8th, 2021.