The Tongue-Eating Louse (Cymothoa exigua)

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Cymothoa exigua is nightmarishly known as, “the tongue-eating louse”. Many a fisherman have discovered a very unwelcome hitchhiker in the mouth of their snapper catch.

In reality, C. exigua doesn’t really eat the tongue. It sucks blood through its front claws and eventually kills the fish’s tongue. After the tongue falls off, it then attaches to the leftover stump, effectively taking the place of the fish’s tongue. C. exigua then feeds on blood and mucus. Yummy!

The Tongue-Eating Louse (Cymothoa exigua) cut-away

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Males can turn into females at a particular time in its life-cycle. Usually that’s once they have a nice permanent spot on the tongue and have grown to a particular size.

They are aquatic relatives of the pill-bug, aka, wood louse, and roly-polies . You can definitely see the family resemblance below. This shouldn’t be surprising however as all insects evolved from aquatic arthropods anyway.

A pill-bug, relative of The Tongue-Eating Louse

Image Courtesy:  Peter J. Bryant

They are cousins of Giant Isopods too (see below). But thankfully, they don’t get THAT big! Phew! Why the “phew”? Because Giant Isopods are vicious, and have been known to attack and eat small sharks! Click here to See:

A Giant Isopod - cousin to The Tongue-Eating Louse (Cymothoa exigua)

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Isopods are generally found off the east coast of the Americas but some have been found in the Atlantic as well. The tongue replacing variety may even be seen in your favorite reef fish! Ohh, this explains why Marlin sounds as if he has something in his mouth. Yes we know, we’ve ruined ‘Finding Nemo’ for you. You’re welcome. 🙂

The Tongue-Eating Louse in the mouth of a clown fish. Yuck!

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Film Footage: The Bay: All Rights Reserved: Lionsgate Films

Film Footage: The Bay: All Rights Reserved: Lionsgate Films


In 2012, a film was released called, “The Bay”. The Plot? Mutant Cymothoas!!

Film Poster - Xray with cymothoa in human mouth

Image Source: Theatrical film poster, wikipedia

… two researchers find a staggering level of toxicity in the water, they attempt to alert the mayor, but he refuses to take action fearing that he will create a panic. As a result, a deadly plague is unleashed, turning humans into hosts for a deadly, mutant breed of the parasite Cymothoa exigua.






Do you want to learn more? Find out what eats C. exigua and gives affected fish a fighting chance. Check out the video below!


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