We had the same thing down in Solomons this last weekend. I was beginning to wonder if it was residue from jet fuel (they were doing touch-and-gos at Pax River NAS most of the time)...
But then we did have a boatload of the small mosquito-like (but non-biting) bugs swarming all over the place, too. I forget what those are called...
Chesapeake Bay, USA