Tongue-eating louse

Kingdom: Animalia

Phylum: Arthropoda
Class: Malacostraca
Order: Isopoda
Family: Cymothoidae
Genus: Cymothoa
Species: Cymothoa exigua
Conservation Status: Not Evaluated
Common Name: Tongue-eating louse

The tongue-eating louse is a strange white parasitic isopod of the Cymothoidae family, commonly found off the coast of California. The parasite is best known for replacing the host's tongue with itself!

The species is quite widespread and can be found from the Gulf of California south to north of the Gulf of Guayaquil, Ecuador. It has been recorded in waters ranging from 2 metres (6 ft 7 in) to almost 60 m (200 ft) deep.

Tongue eating louse description
The parasite has a white segmented body, with a length of 3 to 5 centimetres (1.2 - 2 in). Females are 8 - 29 mm long (0.3–1.1 in) and 4 to 14 mm (0.16–0.55 in) wide. Males are 7.5–15 mm long (0.3–0.6 in) and 3-7 mm wide (0.12–0.28 in) in width.

Tongue eating louse life cycle
The species has a quite bizarre parasitic lifecycle. The parasite begins its life cycle by first entering the victim's body through the gills. Females attach themselves to the tongue while males attach on the branchial arch (gill arches) beneath and behind the female.

Once established, the parasite immediately starts to feed on the tongue's blood using its front claws (from the main artery), which gradually atrophies. Slowly but steadily the parasite gets bigger and bigger. Eventually, it replaces the fish's tongue by attaching itself to the muscles of the tongue stub.

Fish with tongue fully replaced by Cymothoa exigua

It appears that the parasite does not cause any other damage to the host fish. Other than replacing the tongue, the parasite causes no other known harm to the fish-host. Actually, the host continues to use the parasitic "tongue" just like its old one, to grind food against the tiny teeth on the roof of the mouth.

Once the tongue is replaced, some individuals feed on the host's blood while others feed on fish mucus.

The tongue-eating louse is currently the only known parasite to replace a host's organ in its entirety with itself.

Tongue-eating louse, removed from host

Tongue Eating Louse Hosts
Currently, Cymothoa exigua is known to parasitize a total of eight species in two orders and four families of fishes. Specifically, it parasitizes on 7 species of the order Perciformes:

• 3 snappers (Family: Lutjanidae)
• 1 grunt (Family: Haemulidae)
• 3 drums (Family: Sciaenidae)

And one species of order Atheriniformes, a Atherinidae grunion.

Tongue eating louse removed from host

Tongue Eating Louse Reproduction
The species exhibits protandrous hermaphroditism. They first mature into males, but then switch sex and become females. The process begins when more than one tongue-eating louses enters a fish’s gills. The first to enter matures into a male, but when the second one appears, it stimulates the first one to become a female. The female then crawls from the gills up through the throat and attaches itself to the tongue. The second one remains a male so that they breed sometime in the future.

Credit: Image copyright of Matthew R. Gilligan,
Savannah State University

Is it dangerous?
No, this small creepy creature is harmless. Like all parasites, it only has a really small spectrum of hosts and humans just aren't among them. Still if you ever see one, don't pet it or something cause it has a really strong bite.

Tongue eating louse Interesting Facts
- In 2013 in Puerto Rico, the tongue eating louse became the leading subject of a lawsuit against a large supermarket chain. The customer claimed to have been poisoned by eating an isopod cooked inside a red snapper. However, the case was dropped on the grounds that isopods are not poisonous to humans, not to mention that some are regularly consumed in certain parts of the world.
- There are more than 40 distinct species of Cymothoa, however only Cymothoa exigua is known to consume and replace the host's tongue.
- Cymothoa exigua was the main star in the 2012 film "The Bay". The film features a population of tongue eating louses that grows to enormous proportions due to toxic wastes. The resulting species soon begins to infect the residents of a small town on the Chesapeake Bay. Click here if you want to buy the movie.

Video showing three specimens

References & Further Reading
-  A. Ruiz-L. & J. Madrid-V. (1992). "Studies on the biology of the parasitic isopod Cymothoa exigua Schioedte and Meinert, 1884 and its relationship with the snapper Lutjanus peru (Pisces: Lutjanidae) Nichols and Murphy, 1922, from commercial catch in Michoacan". Ciencias Marinas 18 (1): 19–34. doi:10.7773/cm.v18i1.885.
- Brusca, R., & Gilligan, M. (1983). Tongue Replacement in a Marine Fish (Lutjanus guttatus) by a Parasitic Isopod (Crustacea: Isopoda) Copeia, 1983 (3) DOI: 10.2307/1444352
- http://www.wired.com