Working its way up the property ladder, when a crab has outgrown its shell it tries a bigger shell. Sometimes the new shell is too big and the crab returns to its old shell. It waits for a second slightly bigger crab to come along who is a perfect fit for the bigger shell. It will then try the discarded shell of the second crab, which is more likely to be a good fit. Chains of up to 20 hermit crabs can form, each holding onto one another, waiting for the crab ahead to upsize!