An unsuspecting worker ant in Brazil's rainforest leaves its nest one morning. But instead of following the well-worn treetop paths of its nest mates, this ant stumbles along clumsily, walking in aimless circles, convulsing from time to time. At high noon, as if programmed, the ant plunges its mandibles into the juicy main vein of a leaf and soon dies. Within days the stem of a fungus sprouts from the dead ant's head. After growing a stalk, the fungus casts spores to the ground below, where they can be picked up by other passing ants.
This strange cycle of undead life and death has been well documented and has earned the culprit the moniker: “zombie-ant” fungus—even in the scientific literature. But scientists are just learning the intricacies of this interplay between the Ophiocordyceps parasitic fungus and the Camponotini carpenter ants that it infects. Fossil evidence implies that this zombifying infection might have been happening for at least 48 million years. Recent research also suggests that different species of the fungus might specialize to infect different groups of ants across the globe. And close examination of the infected ant corpses has revealed an even newer level of spooky savagery—other fungi often parasitize the zombie-ant fungus parasite itself. “We have advanced a great deal in understanding how the fungus controls ant behavior,” David Hughes, an assistant professor of entomology and biology at The Pennsylvania State University, says. Every few months scientists are discovering yet another peculiar trait that, added together, make this parasite one of the most insidious infections—or perhaps that honor goes to the parasite that ultimately kills the killer parasite.