From The Smithsonian:
Some of the most successful zombie-masters are fungi from the genus Ophiocordyceps. The parasites infest many kinds of arthropods—from butterflies to cockroaches—but it is among ants that the fungi’s ability to control other beings’ behavior is most apparent. One prototypical scenario is found in Costa Rica, where infected bullet ants (Paraponera clavata) climb to a great spore-sprinkling height before the fungus erupts.
In the jungles of Thailand, the fungus Ophiocordyceps unilaterius parasitizes Camponotus leonardi ants, which forage on the ground and nest in the canopy. When infected, these ants shamble toward “ant graveyards,” where they bite down on the undersides of leaves, anchoring their fungus-infested husks at a level of the forest with just the right humidity and temperature to allow the fungus to grow properly. When Sandra Andersen of the University of Copenhagen and colleagues placed the bodies of infected ants higher in the canopy, the parasites grew abnormally, and infested ants placed on the ground were eaten by other insects. “The fungus is sensitive to UV light, and the heavy rainfall in a tropical forest would most likely also be able to damage the fungus,” Andersen says. “The position of the ant on the underside of the leaf limits the exposure of the parasite.” The fungus drives the ants to seek out specific places to die that best benefit the growth of the fungus.
Ophiocordyceps-like parasites have been manipulating other organisms for millions of years—their disturbing behavior has been preserved in the fossil record. Forty-eight million years ago, during the global hothouse epoch of the Eocene, the place now known as Messel, Germany, was draped in a lush, semitropical forest. Archaic primates scrambled among the trees; cousins of early horses browsed; and an Ophiocordyceps-like fungus caused ants to put a death grip on leaves just before the infesting fungus fully overran their bodies. Exceptionally preserved fossil leaves from the Messel quarry show the same pattern of leaf scars made by some living ant species when they have become fungus-controlled zombies.