Sacculina Carcini Feminizes Male Crabs

A parasitic barnacle called Sacculina carcini infects crabs and takes control of their bodies in a remarkably sophisticated way. Once inside its host, the parasite alters the crab's hormones and behavior, encouraging the development of feminine traits that help the crab care for the barnacle's eggs. Infected male crabs may begin performing the same egg-tending behaviors as females, even though the eggs belong to the parasite. The sex change is permanent, and male crabs often retain these changes even if the barnacle is later removed.

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