Brood XIX (also known as Brood 19 and The Great Southern Brood) is one of 15 separate broods of periodical cicadas that appear regularly throughout the southeastern United States. Every 13 years, Brood XIX tunnels en masse to the surface of the ground, lays eggs, and then dies off in several weeks.
We are in the midst of their emergence now. Every morning on the trees you can see them, having crawled up out of the ground during the night. They molt, then fly up into the trees later in the day.
So far, it doesn't really seem all that bad. I had visions of swarms of these things everywhere, but in reality I haven't noticed them very much. You see them on cars and sidewalks, but you could walk for miles without stepping on more than one or two. They aren't all that loud now either. Perhaps that will change. They should be around for six weeks or so.
Here is a nice video from Nashville that gives you the idea of what's going on:
Here is David Attenborough (always great!) talking about 17-year cicadas. These look very similar to the ones we have, but seem to have a creepier whooping sound.