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.
Roguerat's advice about using only a wisp of a wisp is good stuff.
There's not one ounce of fat on that bug...He's just built like a fire-plug. :) He is the Jake LaMotta of mayflies...