These Creepy Little Creatures Live Inside the Mouths of Fish, Replacing Their Tongue

While we at Earthly Mission have previously covered some truly creepy marine creatures, such as the Atlantic wolffish, or the sarcastic fringehead, the tongue-eating louse may top it all off when it comes to creepiness.

The Cymothoa exigua, or the tongue-eating louse, is an isopod (a group of animals, which also includes crabs and shrimp) that spends most of its life inside the mouths of different fish. They are known to remove the tongue, and replace it with themselves. In fact, the tongue-eating louse is the only known parasitic creature that functionally replaces an entire organ of its host species.
Female lice can grow to about an inch (2,5 centimeters) in length, and males usually only reach half that size. However, there’s a twist: every single Cymothoa exigua starts off as a male, but once they set themselves in place inside a fish and complete their maturation process, they switch sexes, and transition into a female. This only happens, though, if the spot isn’t already taken by a female.

The tongue-eating louse kicks off this parasitic journey by entering the fish through its gills (this is actually how most fish parasites get into their hosts). After successful entry, the louse climbs to the base of the tongue and prepares for its long stay inside the fish. First, it clamps onto the tongue with its strong legs, securing itself in the fish’s mouth. Now, this is where it all gets nasty: the parasite pierces the tongue, which severs the blood supply in the tongue. This causes the atrophy of the fish’s tongue, which eventually falls off, leaving the fish with just a stump. The louse then attaches itself in place of the destroyed organ, acting as a prosthetic tongue for the fish, and feeding on mucus and blood.