Braiiiiiiins

For reasons beyond my geeky comprehension, zombies are kind of the thing right now. There's The Walking Dead, Zombieland, World War Z, I am Legend, and my personal favorite, Plants vs. Zombies.

"Get ready to soil your plants"
Seriously. Addicting. Game.

I may not understand the fascination with zombies, but at least it's better than emo vampires. No matter what form you see a zombie in, from cartoonish to gory, they all want the same thing: your brain. In the natural world, there exist real instances of organisms that target the brains of other living things, turning them into mindless minions to do their bidding. So get out your crossbows and wall-nuts and prepare for some true biological warfare.

Toxoplasmosis: Fear No Death

Toxoplasmosis is a protozoan parasite that infects most species of birds and mammals, including humans. In humans, Toxoplasmosis affects the brain by causing schizophrenia and behavioral changes. However in mice, the changes are even more creepy. Mice infected with Toxoplasmosis lose their fear of cats. What's more, they actually become attracted to the smell of cat urine. Despite the variety of hosts for Toxoplasmosis, it can only sexually reproduce in the guts of cats. By changing the behavior of mice to make them attracted to cats, Toxoplasmosis is essentially guaranteeing a front-door delivery to the stomach of a cat where it can successfully reproduce. Even worse, the affects on a mouse's brain appear to possibly be permanent, even if a mouse is cured of the infection.

Euphalorchis californiensis: No "Safety Dance" Here

Euhaplorchis californiensis (let's call it EP for short, shall we?) is not a protozoan like Toxoplasmosis, but rather a worm. A worm with an agenda. This worm must pass through three hosts in order to complete its life cycle. In the warm refuge of a bird's gut, the worm produces its eggs, which are passed out in the droppings of the bird. Those that are lucky enough to land in water are gobbled up by unsuspecting horn snails. Now inside the horn snail, the eggs hatch

This EP larva just wants to hug your brain
(if you are a killifish that is).

into young larva, which decide to take up residence for a while, rendering the snail sterile in the meantime. Eventually the larva figures it should grow up and make something of its life, and leaves its gastropod home. The larva finds its next home: a California killifish. It enters in through the fish's gills and makes its way up to the brain, where it forms a cyst and directs the fish to swim close to the water's surface, wiggling, convulsing, and jerking in order to attract the attention of a

hungry shorebird. California killifish infected by EP are up to 30 times more likely to be eaten than healthy fish. Once inside the gut of the bird, the worm larva finally matures and lays its eggs, and the life cycle is complete.

Lancet Liver Fluke: Werewolf-Zombie Ants

The lancet liver fluke's story is similar to that of fellow worm EP; there are three hosts, one of which is a snail, and another host must be eaten in order to complete the cycle. The eggs of the lancet liver fluke come from the dung of a cow or sheep, which are consumed by a land snail. Eggs hatch in snail, hang out for a while, and are excreted (told you it was familiar). This time the next host is an ant, that becomes infected when making a meal out of snail slime. However the ant doesn't just go and find its way to a cow and do some sort of shimmy to get eaten. Instead, in a cool of the night, the ant in its zombie-like state makes its way to the top of a blade of grass, clamps on with its jaw...and waits. After all, cows eat grass, not ants. 

Photo courtesy of http://bugtracks.wordpress.com/2011/07/17/mind-control/

But there is an interesting, werewolf-like twist to this tale. If the ant is not eaten immediately, it returns to life as usual with the rest of its uninfected colony come morning. It only lives its double life as cow bait at night. Once the fateful night comes, the lancet liver fluke can complete its life cycle in the belly of the cow or sheep.

Human zombies have a pretty sweet deal compared to the real versions you find in nature. With humans, you become a zombie, then you live out the rest of your zombie life munching on the brains of the slow, stupid, and unarmed...well, until someone hacks your head off with a machete anyway. For the victims of parasites, however, their zombie-like form is a mere transitional state to a gruesome death beyond their control. No brain munching, no scaring teenagers making out in cars, no dancing with Michael Jackson. If reading about these parasites has taught me one thing about surviving the zombie apocalypse, I think it's this: look out for snails.