The Tongue-Eating Louse (Cymothoa exigua)

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 their tongue. It sucks blood through its front claws and this 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 continues to feeds on blood and mucus. Yummy!

Image Source: emgn.com

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.

Image Courtesy: Peter J. Bryant

Roly Polies and Cymothoa exigua are cousins of Giant Isopods (see below).

Bathynomus giganteus. Image Source: www.trilobites.info

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 always sounds as if he has something in his mouth. Yes we know, we’ve ruined ‘Finding Nemo’ for you. You’re welcome. 🙂

Image Source: kids.nationalgeographic.com

They have been featured in movies too!

Image Source: Theatrical film poster, The Bay, wikipedia

Synopisis: … 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.


I hope you enjoyed this segment of Organism of The Day! Enjoy the clip below of a giant isopod playing with a shark....... with its mandibles.

Bathynomus giganteus, aka Giant isopod attacking a shark.


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