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.
"The clay substrate inhabited by Tortopus is always firm, nearly always vertical, and usually exposed to swift water."
McCafferty (1975) collected nymphs in hard clay banks approximitely three feet below the water surface in the Wabash River in Indiana. He found the clay banks to be honeycombed by Pentagenia nymphs in the same manner that the banks of the Savannah River are honeycombed by Tortopus.