The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
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.