A hermit crab’s abdomen is soft and vulnerable so a crab requires a shell for protection. A crab can go completely into a shell as a defense against predators. A shell also protects a hermit crab from drying out. Water is stored in the shell to keep the crab moist and to aid in breathing.
Hermit crabs use the shells from land or marine snails. A crab picks it shell based upon size, weight, and space. Broken and damaged shells will not usually be used. Once a shell is found, a crab will modify it by removing parts of it to make it roomier or to create a larger opening.
Multiple shells should be made available for your pet hermit crab. Be sure to supply shells without cracks or holes. Use natural shells and avoid painted shells. Paint can chip away from wear or from your crab modifying the opening to his shell. Some of this paint may get ingested by your pet. Even though the paint is supposed to be non-toxic, eating paint is never a good thing. There are many natural and safe shells available at pet stores.
In order to grow, a hermit crab has to shed its exoskeleton. This process is called molting and happens about every twelve to eighteen months to adult hermit crabs and more frequently to juveniles. When a crab molts, its exoskeleton splits and it wiggles out of the old exoskeleton. Do not remove the old exoskeleton.
The claws and body of the hermit crab are soft and vulnerable during a molt. A crab will hide in his shell for protection while molting. A hermit crab also stores water in his shell and the water helps prevent the crab from drying out. Some crabs bury themselves while molting as added protection. A crab can remain buried for over a month during the molt. Do not disturb a crab for at least a month while it molts.
When the new exoskeleton hardens and the hermit crab emerges, it may eat all or part of the old exoskeleton. You should have alternative shells available for your crab after a molt. He may not always need a new shell, but having them available will aid in your pets well being.
Autotomy is when an animal can cast off a limb or appendage as a defense mechanism. A hermit crab’s legs have break points at the joints. If a crab’s leg or claw is grabbed it can be broken off giving the crab time to escape. If a leg is broken off, the muscles at the joint contract preventing blood loss.
A hermit crab can regrow a missing limb when it molts. Each molt will restore a portion of the lost limb. It may take several molts for the appendage to return to its original size.