Mine may have just blundered in out of curiousity. We had them running all over in the hayfields when we were picking up broken bales, so for entertainment we had a spearing contest with our pitchforks! Very difficult! In the winter they make tunnels just under the soil surface, and when the snow melts there are humps (like pipes on the ground) running everywhere! They might have tunneled up into the raised beds, so putting hardware cloth on the bottom would keep them out.
