In this week’s instalment of Freaks of Nature, we’ll take a look at the Cymothoa exigua, an apt name that doesn’t exactly roll off the tongue.

Cymothoa exigua, a parasitic sea louse, is like something out of Aliens. It inhabits the waters of the eastern Pacific, stretching along the West Coast of the Americas from California to Peru.

The female louse enters the fish through the gills and clamps onto the victim’s tongue while her mate faithfully follows her and latches on to the gills. She extracts the blood from the tongue through her claws, causing it to wither and fall off. She then reattaches to the remaining stub and assumes the role of a fully functional tongue.

Its preferred host is snapper, but it has also reportedly taken up residence in the mouths and gills of various other species such as drum, grunion, and grunt.

Recent reports suggest that the range of C. exigua may be expanding and climate change is likely to blame.
What is the function of a fish tongue, you might ask. In contrast to mammals, it helps push food back into the stomach, instead of forward, until chewing is complete.

Profile of a bloodsucking freeloader

Parasitism is defined as a relationship between two individuals, where one benefits and the other suffers. It’s pretty clear how the fish suffers, but how does the louse benefit?

Once the tongue-eating louse is comfortable in its new position, it continues to feed on the blood and mucus of its host. The protection within the fish’s mouth also provides an ideal breeding site.

The female carries between 480-720 fertilized eggs, only 200 of which are estimated to reach maturity. Although little is still known about the life cycle of this parasite, studies suggest that each female is only capable of reproducing once.

In the case that two males are present, one male will change its sex and become female. This mechanism appears quite a bit more often in nature than you might think.

Invasion of the tongue-eaters

In the 2012 film The Bay, residents of Chesapeake Bay succumb to a mutated version of the parasite which targets humans. Despite this absurd scenario, C. exigua are not harmful to humans unless you happen to grab one and it bites you.

Aside from the obvious stomach-churning factor, these tongue-eating parasites have a relatively insignificant impact on the fitness of their host, humans, and commercial fisheries.