There are a lot of weird looking ocean animals out there, but the tongue-eating louse is the one that takes the cake (or the tongue…). The tongue-eating louse is an isopod, a type of crustacean. It is a parasite, meaning it lives off of another creature. In this case, the tongue-eating louse lives off of a fish, usually one in the perch family.
All larvae are born male. Right after birth, they begin their swim through the open ocean to find a host fish. When they find one, they attach to the gills and begin to grow and develop. Eventually, a younger male will attach to the same host fish. This sends a signal to the older male to move into the fish’s mouth through the gills, where it changes from male to female. Once inside the mouth, the louse will attach to the fish’s tongue using sharp spikes on its legs. First, the louse sucks the blood from the tongue until it withers away. The louse then clamps on to what is left of the tongue, functionally replacing it. The louse is now a permanent resident for the rest of the fish’s life. It is in a prime position to feed on incoming food that the fish eats, along with any excess mucus or blood in the fish mouth. Although unpleasant, this doesn’t kill the fish.
As if that isn’t nightmarish on its own, these parasites still have to reproduce. Once the female is established, the younger male louse attached to the gills will enter the mouth to mate with the female. Afterwards, he returns to the gills, but remains close to the female to ward off other males. Multiple males can be attached to the gills at once, but usually the largest one will be the one to mate with the female.
The female will birth a brood of male larvae from the fish's mouth, who immediately go off to infect more fish. If the female dies, the largest of the male lice will replace her position on the tongue and change to female as well. Male lice only change to female when there are no other lice present (a tongue is available) and a younger male is present. It is unknown exactly why this is. Scientists theorize that the tongue could be a limiting resource to the lice, or perhaps the female emits hormones that prevent the sex-change from occurring in her presence.
The urge to go look in the mirror to make sure your tongue is in fact, still your tongue, after reading this article is completely valid. Fortunately, these lice do not infect humans, so we can all be grateful we’ll never have to be in the same situation as these poor fish.
Cook, C. W. (2012). The early life history and reproductive biology of Cymothoa Excisa, a marine isopod parasitizing Atlantic Croaker, (Micropogonias undulatus), along the Texas Coast (dissertation). Texas ScholarWorks, Austin, TX. https://repositories.lib.utexas.edu/handle/2152/ETD-UT-2012-08-6285.