As hermit crabs continue to molt, they will grow larger, therefore, they will need new and larger shells. Shells are available from many sources from craft stores to online and specialty pet stores. Different crabs prefer different types of shells. Some will change shells as people change clothes, other crabs will find one shell that they like and be very reluctant to let it go even when it becomes too small.
It is recommended to stay away from painted and decorated shells as these can cause sickness in the crabs. Most crabs prefer a natural shell and will appreciate a large selection. A common reason for crab fights is over shells, the only thing a crabber can do is to ensure that there are enough shells of the appropriate sizes in the tank for the crabs to select which they would prefer. Never try to take a crab out of its shell, it will allow itself literally to be torn apart before being taken out. The shell is the crabs’ only real means of protection and needs to be treated as such. In the wild, without the shell the crab will be eaten, remember these crabs all come from the wild.