June is the time to fish "Yellow Sallies" in western Montana, and it looks to me like this is the nymph providing that hatch. There are already a lot of these critters in the Bitterroot River, and last spring I found them in the Blackfoot and the lower Clark Fork (see entries of 4/5 and 4/6/16). It's a nymph, as I noted last year, that looks a lot like Isoperla roguensis, but roguensis has not been found in Montana. What has been found in Montana is Isoperla fulva, and as nymphs I. fulva and I. roguensis apparently cannot be distinguished. (See John Sandberg's "The Isoperla of California (Plecoptera: Perlodidae): larval descriptions and a key to 17 western nearctic species," Illesia, 7:22 [p. 245].) Be neat to find some way to pin down the ID.
But this is the reason I go to Montana at this time of year.
The Skwala! While we didn't take a lot of our fish on dry flies this year, we certainly saw plenty of Skwalas flying around and there were loads of them crawling around on the rocks in the water.
Not all of them were mature, so there will be Skwala fishing this year right into May.