Cymothoa exigua
Image credit: By Marco Vinci [CC BY-SA 3.0], from Wikimedia Commons

Among the numerous jobs I’ve held, perhaps the most embarrassing and ethically troubling was my stint as a telemarketer while in graduate school. I’ve always detested telemarketing and resented being on the receiving end of such calls, but at the time, I needed the money and it seemed like reasonably easy work. The firm I worked for wasn’t calling consumers at home, though: we worked exclusively with the pharmaceutical industry. We called doctors, nurses, veterinarians, and other health professionals, trying to get them to prescribe whatever medication the client was promoting at the moment. (So I sometimes joke that, in a roundabout way, I used to sell drugs.)

One of our projects was to call doctors in areas known to have outbreaks of head lice among school children, and try to encourage the use of an anti-lice product called Nix (which was available only by prescription at the time). And I actually got pretty good at delivering my spiel, convincing physicians that Nix—because it was a crème rinse—was far superior to its leading competitor, RID. But one day I called a doctor in rural New York who sounded particularly curmudgeonly. I had barely gotten two sentences into my sales pitch when the doctor interrupted me and said, “Son, do you know what I do when a kid comes in here with head lice?” I said, “I’m sure I have no idea, sir.” He said, “What I do is I shave off half the kid’s hair. Then I light the other half on fire. When the lice come running onto the shaved side to get away from the fire, I stab them with an ice pick.” Well, I had no comeback for that one, and I had to admit this was someone who had no use for our product. I thanked the doctor for his time and hung up.

Crustacean Got Your Tongue?

Neither I nor any of my immediate family members have had to deal with lice personally, a fact for which I’m grateful. However, nuisance though they may be, head lice are not a huge health risk to humans. The thought of having little blood-sucking parasites attached to your hair and feeding on your scalp is definitely icky, but you’ll live. However, there’s another blood-sucking parasite, a distant relative of the head louse—which is to say a fellow member of the phylum Arthropoda and informally referred to as a “louse”—that does considerably more damage to its host.

Cymothoa exigua, commonly known as the tongue-eating louse, is a parasitic crustacean that has, shall we say, a special relationship with a fish called the Spotted Rose Snapper. It attaches itself to the base of the fish’s tongue and begins sucking its blood. Eventually, the parasite siphons off the majority of the blood flow to the tongue, which then atrophies to a stub. The louse, which grows to be about the same size and shape as the original tongue, remains connected to the stub of the tongue—in other words, it effectively replaces the fish’s tongue with itself. At this point, having lost its blood supply, it switches to a new food source: bits of whatever the fish happens to be eating. Other than having a lousy tongue, the fish appears to be unaffected by the parasite; it can still, in fact, manipulate the louse just as it would its natural tongue. No other parasite has been found to completely replace an organ in the host.

Hitching a Ride

Although varieties of red snapper are found in numerous parts of the world, until relatively recently the tongue-eating louse was only known to infect fish off the waters of California. However, in 2005, a shopper in London purchased a red snapper at a local fish market and found one of these critters where the fish’s tongue should have been. Experts aren’t sure whether this means the tongue-eating louse has migrated eastward or whether it was accidentally imported. In any case, anyone purchasing snapper—anywhere in the world—might want to take a quick peek inside the fish’s mouth before bringing it home, just to make sure there’s not another set of eyes in there.

The tongue-eating louse is not considered harmful to humans. However, if you should unexpectedly find one attached to your tongue, I recommend the following. Using the hot sauce of your choice, set half of your tongue on fire. When the louse tries to run away, have your tongue pierced. That’s almost guaranteed to solve the problem, and trust me, it’s a way better solution than gargling with Nix.

Note: This is an updated version of an article that originally appeared on Interesting Thing of the Day on March 9, 2007.