Scientists have discovered a fungus in Thailand that takes over ant brains, compelling them to mindlessly do the fungus's bidding. We've heard about parasitic ant zombification before, but scientists have no idea how the fungus controls the ants so effectively.
The carpenter ants in question build hives in trees and forage on the forest floors. When they are taken over by the zombification fungus, however, they stick exclusively to the ground. A study reported in the American Naturalist says that this is because the fungus knows it will prosper closest to the ground, so it compels the ants to stay out of the trees.
That's the heart of what is happening here: the fungus somehow forces the ant to do exactly what it wants. The ant first acts as a personal transportation service, conveying the fungus to exactly where it wants to be (the leafy forest floor), and then the ant dies and becomes an abundant food source for the fungus. The fungus even forces the ant to clamp its mandibles onto a desirable leaf habitat, where it stays locked until its death.
Imagine if this happened on a human scale: the fungus would compel you to walk out into a forest, grab tightly onto a tree, and slowly die curled up on the forest floor, probably driving you mad as it ate your brain from the inside. Now if that had been the plot of The Happening, we probably would have been more interested...
Zombie Ants Controlled by Fungus [via LiveScience]