Sponges, my opinion and need advice.

[lolagranola]

Sponges are not necessary at all in the crabitat. They're not harmful but there are much easier ways of providing proper humidity.

DIY humidifiers are cheap and easy to make.

I use a lot of natural moss in my tank which is edible, great at maintaining humidity, cheap and it doesn't need to be constantly sterilized.

[erikleeson]

I have a large moss pit but it always stays wet and if the heat light is over it yeah it raises humidity but it also dries out the moss. I have small pieces of moss on the sand too but it doesn't seem to help. Every odd week I go to a different house where I can only see the crabs four times a week so I need it to be constantly humid.