The Parasitic Worm That Turns Into Disco Zombies

One of the crueler tortures to bestow on a snail is the salt shower, as the behaviorally challenged kid who grew up down the street from you could attest. It’s a horrible death: The salt draws water out of the creature until it perishes from dehydration. Even if you live in Florida, which is overrun with giant foot-long snails that are devouring houses, please do not dispatch them with salt. Snails have enough problems as it is.

Mother Nature, you see, has cooked up an even more sadistic punishment for the humble snail. It’s called Leucochloridium, and it’s a parasitic worm that invades a snail’s eyestalks, where it pulsates to imitate a caterpillar (in biology circles this is known as aggressive mimicry—an organism pretending to be another to lure prey or get itself eaten). The worm then mind-controls its host out into the open for hungry birds to pluck out its eyes. The worm breeds in the bird’s guts, releasing its eggs in the bird’s feces, which are happily eaten up by another snail to complete the whole bizarre life cycle.

It’s an existence that’s as brilliant as it is strange. But while science has known about Leucochloridium for more than a century, it was only in 2013 that biologist Tomasz Wesołowski of Poland’s Wrocław University confirmed the worm is indeed capable of manipulating its snail hosts. (Specifically, amber snails—like many other mind-controlling parasites, it’s highly species-specific, that is, it’s unable to manipulate the behavior of more than one species.)

The lifestyle differences between such worms shows in rather creepy ways just how diverse and opportunistic parasites in the animal kingdom can be. If you can believe it, more than half of all creatures on Earth are in some way parasitic, so we humans are in the minority in the animal kingdom. But if that means not dancing in snail eyes or hanging out in bird intestines, then color me grateful.