Hermit crabs love to switch shells but need larger shells as they grow to maintain adequate body moisture. For a proper fit, the new shell should be larger than the present shell, and the shell opening should be the same size as the crab's large pincher.
They may be named "Hermits" but that name couldn't be further from the truth. Crabs thrive on company and are the most active and entertaining when they co-exist in pairs or in a tree crab community. When increasing the number of hermit crabs, be sure to provide more space for them. They also need a semi-warm and humid environment, 70-75 degrees F.
Crabs also love to climb! They live in trees in the wild so are adept at climbing and moving over rocks, sticks, boulders, etc... Coral and choya wood will encourage activity. Again, be sure they have plenty of room to play!
Crabs will clean themselves if you provide them with fresh water in their bowls. But it is a good idea to bathe crabs. Submerge them in room temperature water for 30 seconds - 1 minute and allow them to air dry. This isn't a necessity if you keep a water dish in the crab tank (which you should be doing) but it just helps them maintain enough moisture for a healthy life.
Crabs need calcium obtained from shell dishes. This can also be obtained by using calcium based sand. They also thrive on pre-mixed hermit crab food and treats, along with a variety of vegetables and fruits. They will bury their food, so make sure you remove all uneaten food in and around the tank to keep it from rotting and producing a smell. We recommend you just give them a pinch of food daily in their food bowl and throw out what they don't eat daily.
Be sure to provide at least 2 inches deep or more sand in the bottom of the tank. Crabs love to bury themselves when they molt. In captivity, hermit crabs often burrow into soil when ready to molt and remain out of sight for a month or more, during which time they consume their molted body, presumably for its calcium content. When several individuals are kept together in captivity, provide material in the tank in which crabs can burrow under and hide. A source of calcium, such as an egg shell, is also desirable.