What could have happened to my hermit crab?

It's Kate could be partly Correct, please follow her advice! but also did you check waaaay back in its shell , it could have surface molted, when they do they hide waaaay back in their shells for protection, you can barely see them if at all, an idea for just in case. You say growing he moved to another shell, but this is not growing until they molt, and that will leave body parts all over if the shed their shell on top of the substrate. LOOK IN THE BACK OF THE SHELL WHERE IT WAS TO SEE IF THERE IS A PINK SOFT CRAB INN THERE, look hard, it is difficult to see them after molting.

Throughout a hermit crabs life it will periodically undergo the process called "Molting". All animals in the Phylum Arthropoda will do this as they all have an exoskeleton unlike Invertebrates who process a interior skeleton. They grow by shedding its exoskeleton.Get one of those plastic carrying cages that are 6"wide X 10" long and 6"deep, they have a lid and do not cost a lot. I put the plastic carrying cage with the molting crab in the regular cage, I make room for them in the main tank. When the molters big claw starts to turn a deep purple it is time to join the others. The molting process is very stressful on the Crab as it can loose limbs or fall prey to predation as in its post molt stage its new exoskeleton is very soft. Some aggressive tank mates will seek out Crabs in molt to eat them so it is best to isolate the molting Crab with its old cast exoskeleton until it finishes the process and eats the old exoskeleton for the additional calcium content to replenish the calcium lost in replacing the old exoskeleton by molting.They are very timid during this time and may cast off appendages due to stress from the thought of possibly being eaten so it is best to handle them as little as possible to avoid this. Put food and water in their tank in close proximity so they have to move as little as possibly because until the new exoskeleton hardens, they are weak from the energy it takes as well as the muscles will pull against the new soft exoskeleton possible causing complications

11.Calcium and Carotene

Cuttlebone is the hard structure in the head of the Squid ,you may purchase them in the bird section of your pet store, ground up they provide an excellent source of calcium as does ground up oyster and egg shells. Post molt Crabs crave cuttlebone and will stand at the dish of ground cuttlebone and eat to their hearts content. Sprinkle a bit in their water is another way to help them get their requirement of Calcium. Carotene keeps your Hermit Crabs color bright , you can get this through carrots and color enhancing fish flakes. Ecuadorian Hermit Crabs seem to suffer from Carotene deficiency more than other species of Hermits

The Ideal humidity level is 65% to 80%, but can do ok with a level of 55% to 60%, proper humidity keeps their gills from drying out and other important soft body parts like the abdomen, this is essential for adequate oxygen exchange.

6.Various Substrates

Which substrate to use is what will make the hermit crabs happy. Many hermit Crab owners use coconut fiber called Eco Fiber and can be found in most pet stores, after researching many websites and hermit keepers the coconut fiber seems to be their first choice and I have used it for aproximenly two years.Coconut Fiber comes in compressed blocks that expands when reconstituted with hot dechlorinated water, hermits love to dig and pick through it for possible bits of food and at molting time hermits will burrow into it to hide and for darkness when a molt is pending. Some Hermit keepers like a small round aquarium gravel ,a pet grade sand or harvested beach sand, both are high in calcium which adds an additional source for their exoskeletons, it is nice although messy when water gets spilled as it is mainly meant to be used dry and that consistancy does not allow hermit crabs to bury and re-surface after molting and to just dig or burrow in. The ideal substrate is moist for burrowing making sand not a good choice in most cases. Course gravel can scratch their exoskeletons or injure soft body parts if it works its way down into their shells. Pure silica sand is not a good choice as crabs seem to do better with either the coconut or sand for hermit crab use and the pure silica sand dust is dangerous if inhaled.

Never use course gravel, wood chips, cedar, or gel, the last three are toxic!Wood chips of pine or cedar type are not a good choice because the sap is toxic and It is hard for them to dig in this material. coconut fiber (also known as Forest Bedding®, Bed-A-Beast®, and Eco-Earth®

Hermit Crab Body Parts

A shell fight happened. Your Hermit Crab's shell got to small for it and was eager and desperate for a new shell so it ripped the other one out of his shell and took his shell. The hermie that was attacked probably won't survive but you have got to make sure you always have big, medium, and small shells in their tank at all times...or a shell fight will start. Make sure your hermit crabs have a 10 gallon tank or more, dechlorined water, fresh an salt water, toys to climb on, hide log to sleep in, and humidity to breath. Hope this helped. If you have any questions email, Kate =D.