Instructions
Keep the hermit crab in a tank that is large enough to house several shells. Hermit crabs are very particular about their shells, so providing just one option may not give them one that they wish to move to. Provide several shells that are slightly larger than the one the crab is living in. You might also encourage him to move shells by giving him a shell that is the same size as his own but is a slightly different shape.
Choose shells that have a smooth natural lining. Mother of pearl shells are popular with hermit crabs because they feel smooth against their bodies. Feel the inside of the shell with a finger to see how smooth the inside really is. The crab will do this with his antennae and will reject one that is too rough.
Give your hermit crab plenty of privacy to make his shell change. Hermit crabs have soft body parts that are housed by their shells. These parts are vulnerable to attack or to injury if the hermit crab is out of his shell for too long. Your hermit crab will likely not want to leave his shell and leave himself vulnerable if there is anyone moving around nearby. Keeping your hermit crab's enclosure in an area of your home that is busy will discourage him from changing shells.
How to Make a Hermit Crab Change Shells
Hermit crabs must change shells occasionally as they grow. Once a hermit crab molts, it will grow larger and need a new home. It isn't possible to force a hermit crab to change its shell, but it is possible to give it the right conditions to do so.