By Matthew Hardcastle
BU News Service

Meet Cymotha exigua, an adorable crustacean of the Cymothoidae family. C. exigua sometimes goes by the common name “tongue-eating louse,” which is a completely unfair mischaracterization: it’s not a louse at all. The tongue-eating part is accurate though.

Cymothoidae contains a number of fish parasites, but none are as charismatic as our C. exigua. This plucky crustacean lives off the western coast of Mexico and Central America. Though its lifecycle is a bit of a mystery, males can be found attached to the gills of at least eight species of fish. When necessary, one of the males will become female, growing larger and making its way to the fish’s tongue, where the real fun begins.

Rather than selfishly sapping the resources of her host and offering nothing in return, C. exigua decides to do her fishy friend a favor by giving it a brand new tongue. Using specially adapted claws, C. exigua draws blood from the boring, regular tongue of her host, until the organ withers away. Then the crustacean makes itself at home by attaching to the muscles on the stub of the amputated tongue.

C. exigua happily begins her new life as a fish tongue, doing all the regular duties of her host’s old organ. All she asks for in return is the occasional sip of blood or nibble of mucus. The fish doesn’t seem to miss its old tongue at all.

You may find yourself wishing for a happy crustacean like C. exigua to come and live in your mouth, but alas they have no effect on humans, apart from a possible love bite if you handle a live one. Snapper with crustaceans for tongues occasionally wind up in fish markets, but C. exigua is not toxic to humans even if you accidentally cook her up.

Truly, C. exigua is one of evolution’s most whimsical and enchanting creations.