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 the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
Described by Ross, H.H. & Ricker, W.E. (1964) New species of winter stoneflies, genus Allocapnia (Plecoptera, Capniidae.). Transactions of the Illinois State Academy of Sciences 57, 88–93.