Odd Behavior

Question
My hermit crab has started a strange habit.  He has decided to build a mound of sand in his coco-hut.  The mound is about 3/4" high.  When I cleaned his crabitat today, I took down his little hill.  As soon as he went back in his tank, he immedeately began to build it again.  Is this behavior related to molting or what?  Its kind of neat to watch, but quite peculiar.  What the heck is going on?

Answer
Digging is something a crab might do before a molt but also just for fun. Most crab enjoy digging for no particular reason (that we've come to understand).

Go ahead and let him do his thing, esp. if he is molting, he needs to be allowed to make his cave.