Cymothoa exigua, also called tongue-eating louse, is a small crustacean that parasitizes fish.
The body length of Cymothoa exigua does not exceed 3-4 centimeters, there are small claws and a shell. Due to its small size, the parasite easily penetrates the gills and attaches to the base of the tongue of the spotted pink snapper.
It sucks blood with the claws in its front, which leads to tongue atrophy due to lack of blood. After that, woodlice replaces the tongue of the fish, attaching its own body to the muscles of the stump of the tongue. The most interesting thing is that the fish can use it in the same way as a normal language, that is, it fully fulfills the functions of the tongue without causing any visible harm to the snapper. This is the only known case where a parasite functionally replaces a host organ.
When the crustacean replaces the tongue, it still feeds on the host's blood, but mostly on fish mucus. Having occupied a "free" place, woodlice parasitize on the same fish until the end of their life. Having reached maturity, she dies, and the atrophied language of the victim never regains its working capacity.
Interestingly, in search of partners, other woodlice even swim into the mouth of the fish, with the parasite living there, where mating takes place. The eggs are laid in a special pocket on the female's belly, from where the hatched Cymothoa exigua set off for free swimming in search of their new home.
Habitat of cymothoa exigua off the coast of California. However, sometimes they manage to swim quite far. In 2005, a fish infected with this parasite was caught in the UK, although this is an exceptional case.
For humans, the parasite is not dangerous, but it can bite your finger if you try to pull it out of the mouth of the fish.