This past week, we have noticed dozens of little dirt piles in our front and back yards. They are about 2-4" in diameter and maybe 2" high. Initially, my wife thought they were caused by ants, but I have my doubts. In addition to there being just way too many of them, the piles don't really look like ant hills. The dirt isn't really fine enough. The other thing is that when you brush away the dirt pile, no ants come charging out and a hole about 1/2"-3/4" is exposed. Anybody got any ideas?