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.
Based on the lack of coloration and the two bars on the last tergite this may be Rhithrogena virilis.
This mayfly was collected from Hungry Horse Creek in Montana on May 12th, 2005 and added to Troutnut.com by Bnewell on June 28th, 2011.