Well, they can appear as early as late August and run into October, but there's no predicting exactly when they will appear or how many there will be. They come out twice a year, and are out now, but so far it's been a light batch.
They don't bite or sting or anything. But if there are swarms of them, they can be annoying. They can eat the paint off your car or rv if you don't wash them off right away and if they swarm, they can smear on the windshield so you can't see to drive. But they are basically harmless.
I have a trip scheduled for the first two weeks of September, and the only thing that would keep me away is a cat 5 hurricane.