Cymothoa exigua, or the tongue-eating louse, is a parasitic isopod of the family Cymothoidae.

[2] Many species of Cymothoa have been identified,[3] and only cymothoid isopods are known to consume and replace the host's organs.

As the parasite is normally found south of the Gulf of California, Mexico, this led to speculation that the parasite's range may be expanding;[10] however, the isopod probably traveled from the Gulf of California in the snapper's mouth after it was caught and imported to the UK, and its appearance in the UK was an isolated incident.

Cymothoa exigua is not believed to be harmful to humans, except it may pinch if separated from its host and handled.

[14] In Puerto Rico, C. exigua was the leading subject of a lawsuit against a large supermarket chain; it is found in snappers from the Eastern Pacific, which are shipped worldwide for commercial consumption.

The customer in the lawsuit claimed to have been poisoned by eating an isopod cooked inside a snapper.

The case, however, was dropped on the grounds that isopods are not poisonous to humans and some are even consumed as part of a regular diet.