NOVA

(whistling) I'm about to introduce you to one of the grossest creatures on earth. It's the tongue eating isopod, cymothoa exigua. 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. Hey. Anyway, the first crazy thing to know about these guys is that they're what's called Protoandritic 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 things get 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. - 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's a photograph of a mouth infesting isopod to prove it. (screaming) 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 the next time you're at the grocery store take a look inside that red snapper's mouth. You might find a tasty treat inside. Ew.