Grimbiosis 1: The Tongue Eating Louse

BlobPerhaps the most strangely cute of all the disgusting parasitic crustaceans, the brutally efficient “tongue eating louse” (Cymothoa exigua) is nonetheless one of the most nightmarish creatures ever discovered. Growing up to just over 2cm in length, this large marine louse is unique in that it is the only known organism with the capacity to completely replace an organ of another creature1.

The disturbing process begins when the louse is newly born, tiny, and immature. The louse is insignificant enough to enter an adult fish, usually a snapper, through its gills. Here, the parasite attaches waits to reach sexual maturity, using the hosts mucus and tiny scraps of food to survive. From there, the female louse move into the mouth of the fish, and secure itself permanently to the fish’s tongue before piercing it and drawing its blood for nutrients. The louse devours the fish’s blood insatiably until the tongue is totally depleted of blood- at which point 90% of the tongue atrophies2, withers, and falls off. From this point onwards, the louse acts as an “organic prosthetic”, performing the same role as the tongue for the fish and, seemingly, leaving the host fairly unharmed- the fish can go on to survive and even thrive, despite its mouth-borne passenger. However, despite researcher’s assurances that the parasite is “benign”, it is hard to believe that the host is not affected by a creature roughly 5% of its size and vaguely resembling an albino Lousewoodlouse living in its mouth.

And then, as if the poor fish has not been violated enough, the louse must then reproduce in order to create even more horrific creatures; meaning that the female will then “do the dirty” with a much younger louse (as a hermaphroditic creature, every individual is born as a male and may only become female after reaching sexual maturity3) inside the fish’s mouth. A few weeks later, the female will then produce a brood of just under 500 hundred eggs, of which around 200 will hatch to produce male lice. Still seem strangely cute?!




1-Brusca & Gilligan, 1983. Available from


2- January C, April 2014, “Isopod got your tongue? (The tongue eating louse)” [ONLINE] Available from [Accessed 17/09/2015]


3- Brusca & Gilligan, 1983. Available from


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  1. Thanks Jasmine, and I’m glad you asked that 😘
    According to the Brusca & Gilligan journal, if the fish dies the parasite will leave the mouth cavity and attach to the outside of the fish- presumably to continue feeding on the corpse, though this has not been confirmed.

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