There is a bug around like the one you describe, that looks like a horsefly to me that will bite the crap out of you. There are very large black flies that can buzz like a bee. They are hard to tell on the wing, so you need to wait for them to rest. Some have lots of coarse black hair. The horse flies have black eyes, the smaller black flies could be “Flesh Flies” and their eyes are red. There are a lot more of them around here than have been in the past, but that might not be what you’re talking about here. Also The carpenter bee will also appear all black but is actually a metallic dark green or dark blue. They are totally unafraid of man but they also only buzz someone to check him/her out. They do this especially if you are near their nest which is a hole in cedar or redwood. I have nests in my shed and they buzz me whenever I go near the shed.
Horsefly, Flesh fly, and Carpenter Bee