In a study conducted by the University of California Berkeley when hermit crabs get into a group (usually 3 more) they end up taking each others shells based on size and dominance. The smallest hermit crab gets evicted from its shell by the bigger crabs.
Hermit crabs use these empty shells as their home and for protection against others. There are about 800 types of hermit crab species and for most of them shells are very easy to come by in the ocean. Now it is a different story for land hermit crabs because there is a shortage of shells for them. The shells for land-based hermit crabs mostly come from marine snails that have been tossed ashore by the waves.
Land based hermit crabs tae these shells and hallow them out and make them about double in size. This meeting of the hermit crabs is to take the most desirable shells from the weaker crabs and there’s not much the weaker crabs can do.