More than 100 miles of the Susquehanna River and its tributaries hold this prolific hatch. Once the White Fly begins in a given area, it usually lasts for about two weeks. If you plan to fish this hatch near Boiling Springs, be prepared for heavy angling pressure. The White Fly goes through an unusual emergence sequence. Males emerge and quickly change from a dun to a spinner.
Females emerge and immediately fly up and down over the stream just a few feet above the surface.
The females, unlike other mayfly species, never change from dun to spinner. At the beginning of the mating ritual, trout often jump out of the water trying to capture some of the mayflies just above the surface. Try dragging your imitation at this time. In that article I suggested that you look for a trout chasing a mayfly, cast a White Fly with over-sized hackle just upriver from the riser, and start dragging the fly. Light brown hackle fibers.