The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
This is another stonefly that lives its nymphal life in the hyporheic zone, flood plain gravels. In this case, the gravels of a small stream, Roy's Creek, that flows into Flathead Lake at the Univ. of Montana Biological Station.