Overview

You’ve probably seen some strange animals in documentaries or real life. But this tongue-eating parasite will definitely give you the creeps: The buglike isopod sucks blood from a fish’s tongue until it detaches, attaches itself to the fish’s mouth, and assumes the organ’s place in the still-living host’s mouth. It’s the stuff of nightmares.

The science and other stuff to know

The parasite, also called Cymothoa exigua, is a parasitic isopod of the family Cymothoidae. It enters the fish through the gills. There are several species of tongue-eating parasites, and many species target one particular type of fish, the same way tropical moths have evolved to feed on specific orchids, according to a study published in the International Journal for Parasitology.

When a group of juvenile isopods finds a fish, they swim into its gills and latch on with their spiky, clawed legs. At this point in their life cycle, all of the isopods are small; however, one isopod will grow larger than the rest. The female will then crawl out of the gills, up through the throat to the mouth where she’ll attach herself to the blood vessels at the base of the tongue.

The female then stays put and cuts the blood vessels in the fish’s tongue. Without blood flow to the organ, the tongue will eventually wither and fall off, leaving the parasite in its place. The parasite will then continue to feast on the fish’s blood and mucus. Surprisingly, this highly invasive activity doesn’t kill the fish. The fish can use the parasite as a prosthetic organ and live with it for years.

Should humans worry?

This tongue-eating parasite doesn’t infect humans, but according to the Centers for Disease Control and Prevention (CDC), there are other parasites that humans can get in their mouths. For example, the Gongylonema infection is mostly caused by the use of polluted water and raw food. Adult Gongylonema worms can live in the human body as parasites for up to ten years, causing signs of local irritation in the mouth cavity, esophagus, and pharynx.

Also, while the Cymothoa exigua are harmless to humans, they can spell disaster for commercial fish farms. When a single species of fish are packed so closely together, the isopods can spread rapidly between them. After a few generations, the water will be infested with blood-sucking larvae such that the fish become anemic.

Since Cymothoa exigua are rather widespread throughout the oceans, they have been frequently found in the mouths of fish we are looking to buy as well. Therefore, you might want to pay particular attention to the mouth of your upcoming meal the next time you’re shopping for fish.