Tongue-eating lice are parasitic isopods that live in the mouths of marine fish such as spotted rose snapper. These parasites are hardly rare and approximately 380 types of tongue eatings isopods have been identified. 

Tongue-eating lice are most often found inhabiting the mouths of their fish hosts, effectively replacing the fishes’ tongues—which is how the parasites got their nickname. Despite the “tongue-eating” part of the name, they do not technically eat their hosts’ tongues. They actually attach themselves in the buccal (mouth) cavity at the base of the host’s tongue and suck blood from the tongue until it shrivels up and falls out. The now tongue-less fish starts using its new mouth isopod as a replacement tongue, while the parasitic “tongue” continues to feed on its host’s blood and mucus. Believe it or not, the fish can survive and get by just fine with a parasite as a tongue.

In an even more bizarre twist, this unusual relationship between fish and living tongue often lasts for years, with the parasite sometimes dying much earlier than the host fish.