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.
Described by Baumann, R.W. & Gaufin, A.R. (1972) The Amphinemura venusta complex of Western North America (Plecoptera: Nemouridae). Contributions to Science, Los Angeles 226, 1–16.