George A. Romero’s classic zombie film Night of the Living Dead begins one afternoon in late winter. As the wind gusts and a thunderstorm approaches, a ’67 Pontiac Le Mans winds up a country road in Butler County, PA, and stops at the Evans City Cemetery. Barbara gets out of the car and finds her father’s grave; then the first zombie shows up. He wrestles her brother to the ground. Johnny’s head hits a tombstone, and he passes out.

After a while, he comes back, but Johnny isn’t himself. The zombie had bit into his flesh and turned him into a member of the undead mob. Together, they stumble into an abandoned farmhouse, where they discover his sister. Barbara is mortified and probably eaten alive. She is zombified.

As it turns out, parasites manipulate the bodies and the brains of their hosts. In life, as in art. They program nervous system cell death in their hosts; they alter the neurochemicals that affect how their hosts act. They starve them; they cripple them; they castrate them; they make them easy prey. The better to propagate themselves.

More than herbivores or carnivores or fungivores or omnivores, parasites probably make up the most common consumers on Earth. As many as half of all known species are parasitic species. Fossilized evidence of parasites is many millions of years old.

And there are many millions of parasites now. From the jungles of Thailand to the marshlands of central Europe, to tropical Africa, to the North American coasts, they affect the morphologies and the minds of their hosts. They turn them into zombies.

Across terrestrial ecosystems, ants are the dominant fauna, and many are parasitized by fungi. Around the time that Charles Darwin’s book On the Origin of Species came out, Ophiocordyceps unilateris, the zombie ant fungus, was discovered on a trip to Southeast Asia by the intrepid Alfred Russell Wallace. Inside an ant colony, workers clean the house to prevent fungal growth, but outside the colony, ants can be easy targets.

When........

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