The fungus, a species of Ophiocordyceps, targets carpenter ants living high in Thailand's rain forest canopy. The parasite hijacks the ants' nervous systems, causing the insects to perform abnormal—and oddly specific—behaviors that help the fungus reproduce.

(Related pictures: "'Zombie' Ants Controlled, Decapitated by Flies.")

In a new study, researchers used microscopes to peer inside affected ants and see how the infection progresses. The team found that the growing fungus slowly fills the ant's body and head, causing muscles to waste away and muscle fibers to spread apart.

It takes about three to nine days from initial infection for the ants to become completely zombified, the team found. At first, the infected ants go about their normal business, residing