The head of a southern right whale bears large callosities (hardened patches of skin) that become infested with colonies of parasites, including barnacles, lice and parasitic worms. Right whales always have a prominent callosity, known as a "bonnet", on top of their snout. Grey whales and humpbacks have the same kind of infestation, but the callosities are spread over their bodies, rather than clustered on their heads.