Allow me to introduce to you, just in case you've never had the pleasure, a biting fly of the genus Chrysops. Commonly known as a deer fly, I prefer to think of it as aggravation incarnate. Yes, it's true, there are a very few animals I just plain don't like (but to be honest, I can appreciate them in context) and this one is tops on that list.
It's not so much that they bite -- they do, and quite viciously -- it's that they torture you first by flying about your head and face, crashing into your ears, flying up your nose, even going behind your glasses. ARGH...makes my blood pressure go up just thinking about it.
But they are sort of pretty when you take the time to look at them...
...just before you squish them!
Addendum: The kind and knowledgeable folks over at BugGuide.net have informed me that the top photo is of a female Chrysops vittatus. Now I can curse them properly and with respect :)