"Shell fights occasionally occur among wild and pet hermit crabs and can often be detected because of chirping sounds. From a position slightly above the defending crab's shell, an attacking crab seizes the defending crab with its walking legs and rapidly rotates it back and forth. While doing this, the attacker's claws are usually inside the opening of the defending crab's shell. This shaking often drives the defending crab from the shell that the attacker wants. Practically leaping out of its shell, the loser waits and enters the victor's shell. Typically, neither crab is harmed and both might get a better-fitting shell." I've seen crabs have sequential shell fights down the 'intra-tank-pecking-order' until the weakest crab was left naked. This was because the air in the tank got so hot that the crabs required a thinner shell to aide in cooling their abdomens. Keep a close watch on the temperature and make sure it does not get too hot.