"Nature reserves the right to inflict upon her children the most terrifying jests,” the playwright Thornton Wilder once wrote. And while he wasn’t pointing the finger at Cymothoa Exigua, specifically – this nightmarish crustacean wasn’t discovered until this century, and Wilder died in 1975 – the description certainly fits. If you’ve managed to get through life without hearing of this aquatic horror, then it might give you a clue to know it is more commonly called the tongue eating louse (we’ll call it a cymothoa exigua for short). Which sounds bad, but doesn’t capture the full horror of this creature’s life cycle.
The Cymothoa Exigua Is A Parasite
Like many of the planet’s most unpopular creatures. Parasitism is defined by Wikipedia as “a symbiotic relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life.” That definition is broad enough to include some astonishingly different creatures, from tiny protozoans to fungi to large mammals like vampire bats.
Much as we may try to avoid thinking about it, humans are certainly not immune to parasites. They are the creatures which cause malaria and there are at least 300 species of parasitic worms which are known to find humans a happy habitat. Nor is this just a problem in the developing world: at least 1 in 20 US citizens host one type of parasitic worm.
Some of the parasites afflicting humans can result in horrific problems, including blindness and elephantiasis. But none of them is quite as freakishly strange as the cymothoa exigua. Fortunately, for us land lubbers, it is an aquatic creature, a tiny crustacean called an isopod which enters certain breeds of fish through their gills. So far, so normal – most fish are invaded by parasites in the same way, and many of them can co-exist without the fish being aware that it’s become a floating hotel.
Cymothoa Exiguas Are Hermaphrodites
However, with the cymothoa exigua, things start to get very strange once they have made themselves comfortable in their new home. cymothoa exiguas are protoandritic hermaphrodites, which means that the adults can change genders. In their standard form, they are males so tiny they can pass through the gills, but once present in the fish, one of the males will typically begin to transition into a female form. Their legs elongate, their claws swell, their eyes shrivel and their body grows immensely larger.
Cymothoa Exiguas Take Over It’s Host Tongue
And no, that’s not the freakish part, gender transition being perfectly common amongst crustaceans and many other animals. What happens next is that they start to live up to their name. The female will migrate to the fish’s tongue and clamp on with its claws, cutting off the blood supply. The fish is unable to do anything to remove the parasite, since scraping it off would also remove the tongue and doom it to starvation. Soon (but, for the fish, probably not soon enough) the tongue will atrophy and simply drop off. At this point it’s presumed that the cymothoa exigua eats the dead organ to earn its name.
No, that’s still not the freakish part. The really strange part is that after the tongue is gone, the cymothoa exigua takes its place. It attaches itself to the stump and from this point on performs the tongue’s duties, such as guiding food into its host’s throat. The two can live together in a kind of symbiotic harmony for the rest of the fish’s lifespan. The cymothoa exigua will feed the fish and in exchange feed off the fish’s blood and mucus. While it’s not been possible to confirm for certain, it seems likely that the death of either will inevitably mean the death of the other.
While the results of this arrangement look absolutely horrifying to human eyes, both creatures seem to make the best of the situation. The fish will continue to eat and mate, just as it normally would, and so will the cymothoa exigua, who will breed with all those tiny males who hopped on board with her at the start of this journey. The fish’s mouth will become a setting of idyllic domesticity for the isopods, who will bring lots of tiny little baby cymothoa exiguas into the world which then drift off in search of their own family bliss in the mouth of another unfortunate fish.
Cymothoa Exiguas Are Commonly Found In Fish We Eat
What fish, you may be wondering, thinking back uneasily to the last fish soup you had. A good question with a regrettable answer. Because the cymothoa exigua actually loves a lot of the fish you love, from snappers to bass, and are common in a lot of waters around North and South America. In other words, if you are a fish fan there’s a very good chance you’ve eaten a cymothoa exigua-infested fish before.
In fact, humans have had very close encounters with cymothoa exiguas. We already said the females can grow large, but if you consider that they can infest a five foot marlin, you can get an idea of just how large they can grow. Inevitably, some humans have decided to test them out as a food in their own right, which seems fair karmically speaking. Unsurprisingly, they taste much like their cousins, the shrimp.
Indeed the cymothoa exigua is, to the best of our knowledge, perfectly safe to eat, although some humans have reported to being pinched by their claws in the attempt. Fortunately , so far, nobody has had their tongue devoured by one and needed to use a cymothoa exigua as a substitute. Or at least, nobody has ever admitted to it.