5 years ago while my husband was working in Round Rock Texas, I heard a buzzzzz buzzzz buzzzz. I looked to my left, to my right, and saw nothing. Then I looked up and saw what looked like a black cloud over my head buzzing. Now I'm in an electric wheelchair due to Muscular Dystrophy and I tell you Jerry Lewis came very close to seeing his cure. I put my wheelchair into over drive and zoomed into the garage. The cloud buzzing floated over the garage and left. My husband came out of the home he was working on and I told him about the cloud of buzzing. I took him over to the spot I first saw it, and we spotted a black and orange bee dead. I looked this bee up on the computer and yes they where killer bees and the news confirmed killer bees were indeed in Round Rock. People have been attacked and 1 person died. So I guess my answer would be bees, because I know I can out run (wheel) them lol.
BTW, I also ran over and killed a snake while in Texas, but that's another story lol.