Seems to me they come and go at will. We've had tons of them some years, and no problem other years. The one year they were really bad, digging up and/or eating my plants, I put a box of D-Con out. They disappeared fast so it seemed to work. I didn't want to chance poisoning any birds or other critters, so I put a box in an area were they were very active, put an upside down flower pot over it with a stake through the drain hole.
Karen
