The worst bugs I've ever dealt with are on Ocracoke Island, in the NC Outer Banks. It's the only place I've ever encountered them. I am not sure what they are, we have always just called them sweat bees. I think they're actually some type of biting fly though. They are metallic green, large flies, and they have a painful bite/sting. I think they are attracted to sweat, but getting out of the ocean when the water dries to a salt film, that seems to attract them too.