I have a large bed in my side yard filled with shrubs and perennials. For the last few weeks, this bed is being terrorized by some sort of nighttime creature and I'm hoping to get some advice on how to get rid of it.

Every couple of days, I find a new hole somewhere in the bed. It is always at the base of a plant so that the roots are being disturbed by the digging. I don't see any pattern regarding the plants that have been disturbed. I've found holes under the following: viburnum, azalea, coreopsis, coneflower, geum, rudbeckia. I would say the holes average about four inches wide and six inches deep.

There is never a mound around the hole, so I don't think it is a mole. It must be rather large in size (i.e. raccoon, skunk) because many of my perennials have also been trampled in a way that a small animal cannot do - they literally look like they have been sat on by a full grown man. Also, none of the plants themselves appear to be snacked on, so its not likely to be something like rabbits.

I should note that we had a grub problem in the bed in the spring and so I did a treatment with beneficial nematodes (in late May). Since that time, the only grubs I've found appear to be dead and I haven't found many. I don't know if this is relevant or not.

Any ideas what is digging up my bed and/or what I can do to get rid of it?