Hermit crab digging

Is it common for hermit crabs to dig in sand? I came home today and there's a pretty big crater in the corner that goes all the way down to the glass on the bottom with a pretty big mound of sand on the right of it. Can I smooth over the sand?

 

My hermits have never dug much, maybe a little to find a tasty bit. Could there be another culprit?

 

All I have in there other than the hermits are a turbo snail and two yellowtail damsels. Plus, I have seen them in the hole.

 

None of my hermits dig that much. But my damsel would take off real fast from a corner of the tank and after so many times of him doing that he eventually flung around enough sand that it dug a hole.

 

I bet it is the damsels. My clownfish digs a hole all the time...fans the sand out with its tail. It seems to be a nesting thing....If I fill it in (during water changes for example) the fish re digs it.