re: Huge gnats that buzz dive at you -- what are they?

It is because you stink.

Swarms of biting gnats have been a bitch this spring. Same about 4 or 5 years ago. I was told that they have a life cycle that skips some years but I don't remember how long the cycle is. The bites can be nasty and cause the tissue to either itch like crazy or to turn black and die then fall off. Very nasty.
2 remedies. There are some repellents that work but aren't perfect. One is called no-Natz and contains rosemary oil and lemongrass oil, and the other is Swamp Gator with rosemary oil, peppermint oil, geraniol, and geranium oil. Both made in Georgia. Once you get bitten, chiggerex works ok to stop the itching. Contains benzocaine. Finding all of these things are hit and miss in drugstores and supermarkets and pretty inexpensive.
Good luck.