Apparently 0 blood type is an attractant for them.
I'm 0 positive and I have 4 electric bug bats at summer camp at the lake. 2 inside and 2 outside the trailer. For a short while last summer, I have to have one in the boat for when I just happened to be close to shore. They found me. Worse at the horseflies. Can't even feel them land - they re huge, but they draw blood. They don't fly very fast though and are easy to fry with the bat.
Good thing about wasps, is they grab the screen and try to sting it. Fries them too.