This is what's left after a hermit crabs molts.Molting--A Time of Growth and Regeneration:
(Source: http://members.tripod.com/~animalcare/hcmolt.html)Hermit crabs have rigid exoskeletons that do not grow as the crab grows. The hermit crab must shed its exoskeleton every now and then as it gets bigger. This is the process known as molting. Molting is strenuous for the crab, and death is known to most commonly occur at this time. Any limbs that the hermit crab has lost since its last molt will be regenerated at this time. Smaller crabs must molt more often that larger ones because they are growing faster. Small may molt as often as every other month; it may be only once a year for a large crab.
When Your Crab Molts: If you know your hermit crab really well, you may notice a change in its personality prior to molting. A few weeks before a crab molts, it will become inactive and may bury itself in the sand until the new exoskeleton hardens. However, inactivity is not always a sign of molting; some hermit crabs are just naturally not as active as others. Also, not all hermit crabs bury themselves when they molt. It's often pretty difficult to predict when your hermit crab is going to molt. The important thing is to take good care of it after it happens.
If you discover that your hermit crab has molted, you should separate him from any other crabs in the cage. Note: The shed exoskeleton will look like the body of a dead hermit crab, so don't discard your pet before you check to see if there is a crab hiding inside the shell! It is probably best to move the other crabs rather than the molting one (so as not to disturb it) into another cage if you have one available. If possible, you can keep them all in the same cage and section off the part that the molted crab and its old exoskeleton is in. It is important that the molted crab is separated from the others because it is extremely vulnerable in this state and cannibalism is sometimes known to occur among hermit crabs; it will also prevent the other crabs from eating the other crab's molted exoskeleton. Until the new exoskeleton hardens, avoid disturbing the hermit crab. It will take about ten days for the new exoskeleton to harden; the crab should remain in quarantine during this time.
The Importance of Moisture: Water is always important to hermit crabs, but especially during molting! The extra moisture will help the crab shed the old exoskeleton. If a hermit crab has difficulty shedding the old exoskeleton, it could die. Therefore, make sure that the cage always has adequate moisture.
The Old Exoskeleton: The old exoskeleton will remain somewhere at the opening of the shell after the crab molts. It is important not to discard it so the hermit crab can be able to eat it (don't be alarmed--it provides the crab with necessary calcium). But if you have accidentally thrown it away, you can supply the hermit crab with calcium by putting pieces of cuttlebone (they are sold for birds in pet stores) in its water dishes.
There should always be extra shells available to your crab
Shells
Hermit crabs occupy snail shells, which not only are needed to protect their soft abdomens but are also used to store moisture, which is extrememly important to the crab. After a hermit crab molts, it will need a larger shell than its previous one. You should always keep several extra shells in the cage so the crab can choose a new one to move into at any time. Make sure all the extra shells are slightly larger than the one the crab has now. The shell's opening should be as large as the crab's largest claw. You should be able to find hermit crab shells in a pet store. Before placing new shells in the cage, wash them out thoroughly. The most effective way to sterilize them is to boil them in water.
This is what a hermit crab looks like when it comes out of it’s shell.
