Family: Cymothoidae

'Fun' Fact:  This creature enters a fish’s body through its gills, attaches itself to the base of the fish’s tongue and extracts blood from the tongue with its claws. In fact, this isopod drinks so much blood that the tongue atrophies away, starved of all nutrients. Then it replaces the tongue by attaching itself to the muscles of the exposed tongue stub. The fish uses the louse as if the parasite were its very own tongue.


This is the tongue-eating louse. This parasitic crustacean latches onto the tongue of its primary victim, the spotted rose snapper, and doesn’t let go. Once it does, the louse sucks the blood out of the tongue, until the organ wastes away. When that happens, the louse essentially becomes the new tongue, attaching its body to the stub of the old organ. It then feeds on the remains of food that the snapper doesn’t completely swallow.

Amazingly, the snapper isn’t harmed too much by the entire process as it continues to live and feed after the louse makes a permanent residence. Though the spotted rose snapper is the louse’s main target, the crustacean has been found sporadically in several other species.


Cymothoa exigua, or the tongue-eating louse, is a parasitic crustacean of the family Cymothoidae. It tends to be 3 to 4 centimetres (1.2 to 1.6 in) long. This parasite enters through the gills, and then attaches itself at the base of the spotted rose snapper’s tongue. It extracts blood through the claws on its front, causing the tongue to atrophy from lack of blood. The parasite then replaces the fish’s tongue by attaching its own body to the muscles of the tongue stub. The fish is able to use the parasite just like a normal tongue. It appears that the parasite does not cause any other damage to the host fish.


Isopods are crustaceans, like lobsters and crabs. This particular isopod happens to live in the ocean and is a parasite. It’s a sort of…marine louse. Only it’s way creepier.

Anyway, the first crazy thing to know about these guys is that they’re what’s called “protandric hermaphrodites.” That means that when they’re adults, the males can become females. These isopods infest fish, so what happens is that a number of juveniles enter through the fish’s gills, and all mature into males. Then, one of the isopods will become a female and that’s when everything gets really freaky.

The female will crawl into the fish’s mouth, and attach herself to the base of the fish’s tongue using her back legs. Then, she’ll suck blood from the tongue until it withers and dies. This procedure is quite unpleasant for the fish, but it doesn’t kill it. In fact, it starts using the parasite like a prosthetic tongue! Meanwhile the isopod just continues to hang out in the fish’s mouth, sucking its blood, or feeding on fish mucus.

We don’t know a ton about the parasite’s life cycle, but based on other mouth-infesting isopods (and yes, there are others) the female may even mate while in the fish’s mouth with male isopods living in the fish’s gill chamber!

I know this doesn’t sound real, so here is a photograph of a mouth-infesting isopod to prove it.

Thankfully, these guys don’t infest humans. But, they do infest fish that we eat.Cymothoa exigua has a preference for snapper, and other mouth infesting isopods prey upon mahi mahi or barramundi. So, next time you’re at the grocery store, take a look inside that red snapper’s mouth. You might find a tasty treat inside


also read more about the woman who found on in a fish she bought from a supermarket.

Tongue Eating Louse (Cymothoa exigua)

A pair of ocellaris clownfish (Amphiprion ocellaris) are hosts to the tongue eating louse. The parasite enters the fish through its gills where they extract blood from the tongue. It then replaces the atrophied tongue, attaching its own body to the stub. The fish is able to use the parasite just like a normal tongue. This is the only known case of a parasite functionally replacing a host organ.

Image: © William Tan


Cymothoa exigua

Cymothoa exigua, or the tongue-eating louse, is a parasitic crustacean of the family Cymothoidae. This parasite enters fish through the gills, and then attaches itself to the fish’s tongue, which it destroys by extracting blood through the claws on its front, and then attaches itself to the stub. Females are 8–29 millimetres long and 4–14 mm in maximum width. Males are approximately 7.5–15 mm long and 3–7 mm wide. The fish is able to use the parasite just like a normal tongue. It appears that the parasite does not cause any other damage to the host fish. Cymothoa exigua is quite widespread. It can be found from the Gulf of California south to north of the Gulf of Guayaquil, Ecuador. This isopod is known to parasitize eight species in two orders and four families of fishes. It is currently believed that species is not harmful to humans unless picked up alive, in which case they can bite.

photo credits: wiki, wiki, firsttoknow, zooeco

tongue-eating louse head found in can of tuna. this louse is an isopod, like a wood louse, and is known to cut off the circulation from the tongue of a fish, causing the tongue to eventually fall off (a painless process for the fish). once this happens the louse attaches its body to the muscles left in the stub of the tongue and acts as the tongue - even allowing the fish to use the louse as a functional tongue.

from here and here

Tongue-eating louse (Cymothoa exigua) is a parasitic crustacean of the family Cymothoidae. This parasite enters fish through the gills, and then attaches itself at the base of the fish’s tongue.