The Importance of Hermit Crab Shells
The shell is not part of the Hermit crabs body but a temporary home. Hermit crabs have long curly abdomen that stick out from the rear of its body. This abdomen is not protected by an exoskeleton thus it needs the shell for protection. The shell will also help store water for moistening his gills and for drinking. Hermit crabs grow and look for new shells for their home.
You should supply your Hermit crab with plenty of shells. Be sure to choose only whorled shells with a round opening, not merely a slit or elongated opening. A Hermit crab on average will change his shell 20 times during his life. It is also good to purchase a few shells when you first buy your Hermit crab(s) so that you can refer to the size you need.