Why do my hermit crabs eat their sponge?

Question

I have 2 large hermit crabs and have had to purchase several sponges for them because they eat them (I do see a few extremely small pieces of sponge in their tank, but not enough to equal what is missing from the sponge, that's why I think they're eating them). There is plenty of food in there, so that's not the problem. Has anyone else had this problem, if so, do you know why they do this?

Answer 1

basically they are trying to suck out all the water that they can. If it is try, they start munching on the sponge to get that last little bit of water out.