Been my experience that the tiny little ones you can't even see leave the biggest nasties welts. Big yellow circles the size of an old time silver dollar. Must be because they're fresh from the swamp water.

But we have horse flies down here in Memphis that will drill through kevlar if they have to to get at ya!

You feel THEM the instant they bite, and then you feel it even MORE so. They're about three quarter of an inch long, and I think the medical profession designed their square hypodermic needles after them. You know - the big corkscrew ones...