Deer fly, horse fly, moose fly. Those are hypodermic needles with wings. Usually one at a time, and they fly circles around your head before sneaking up in stealth mode, and you don't feel them till they've jabbed their needle into you. Hurt. Oh man, those things hurt.
Way, way worse! They surround you in a swarm. They love to crawl into secluded dark places: up your nose, in your ears, under your hair, up your pant leg, between pants and shirt, down the front of your shirt, into your bra, in your eyes. They love to get between my eyes and glasses, then ping back and forth in that space until they land in my eye. I once had one fly down my throat. I choked and gagged on it so bad that I peed my pants. Now, that's the ultimate insult! The worse thing is that these suckers are so irritating that my skin welts up even if all they do is land on me. They don't even have to bite before I'm in total skin misery.
A bit of a spoof that gets lots of folks totally wound up every season at the height of black fly season:
http://msmomainmaine.blogspot.com/2014/01/maine-blackfly-breeders-association.html