Moved from ID Request.

Thanks for all the interesting info on this species, Lloyd!

This is a male Ephoron leukon in the process of molting into an imago immediately before mating. The males are often seen flying with the subimaginal shuck still clinging to their tails. The females mate and die as subimagos. These are commonly known as "white flies," and they emerge in great numbers along much of the Susquehanna. Occasionally, they have been known to cause a mild nuisance in some places on the river by requiring the closing of highway bridges during their emergence.

They are fascinating and unusual mayflies, and they provide a feast for many river fishes. Smallmouth bass and even channel catfish feed heavily on the surface during the emergence and the egg-laying flight that follows shortly thereafter. The adults are extremely short-lived, even for mayflies. They emerge in the evening and do not live to see the following dawn.

Looks like it could be a Mayfly. They come out in incredible numbers at times.