Need help identifying critter digging holes and damaging my trees

I'm not sure what, exactly. I'm not even positive it's the same animal doing both things, but I noticed both at the same time. Based on my internet research, the holes might be dug by a skunk, but I can't find anything about skunks damaging trees like this is doing. I haven't ever seen any skunks around here, but the other night I looked out on the deck and thought I saw a skunk tail, but then saw Spare eating and thought it was him. Now I'm really not sure.

The holes are too small for a vole and not large enough for a groundhog. It doesn't look like a mole's hole and there aren't any tunnels around. Whatever it is, is apparently digging for grubs, because there are several holes and none of them lead to anything.

So here are the pictures. Any ideas?? If you know anyone who might be able to help, you can send them the whole album with this link:

http://picasaweb.google.com/jamieannharman/041208CritterDamageToYardAndTrees

Now for the pics.

The biggest hole with my foot for size comparison



Two of the holes (one on the left is the one in the other picture)



This is the oak tree right beside the deck. Husband keeps wanting to top it off or cut it down but I am against that, because I love this tree. I hope this doesn't kill the tree. :( That hole was not there before. To the bottom left, I pulled the bark away and found a bunch of pill bugs (roly poly bugs). I don't know if that's what they were after or some other grub or larvae.



An oak tree in the back of the yard. This hole is pretty large and may not be a completely new hole.




This is a dead oak tree in the woods over to the side.