Thanks.
Do they nest in the ground as well?
Yes, they certainly can. My son mows grass, started this past summer. And my friend mentioned to me to have him watch for bee nests in the ground; they get very upset if you stir up their nests. And sure enough, he says he runs over them periodically, but none have swarmed him yet.
http://gocb.wordpress.com/2007/03/26/mating-ground-bees-on-upper-flat-march-25-2007/