We all view reanimated corpses as a fictional, yet nevertheless, terrifying phenomenon. We’ve seen different types of zombies in The Last of Us, The Walking Dead, World War Z, and even Shaun Of The Dead. What if I told you that the dead may already be walking among us?

Enter Ophiocordyceps Unilateralis, commonly referred to as the “zombie fungus.” Found in tropical rainforest ecosystems, this pathogen mainly afflicts ants of the tribe Camponotini, sometimes referred to as carpenter ants. To describe how the fungus works, we will label the first infected ant of a colony as “Patient Zero.” Initially entering via the bloodstream, Ophiocordyceps exist as single cells that undergo mitosis to multiply. At a certain point the individual cells begin working in unison, forming tubular connections that enable inter-cell communication and the exchange of nutrients. These bands of cells take over the interior of the Patient Zero, fusing with the organism to create a pseudo-superorganism. It is not obvious at first that Patient Zero is infected; in fact, the colony often remains oblivious to its infection. Interestingly, the fungus does not actually infiltrate the brain of Patient Zero; rather, it surrounds the brain and muscles to control the ant. Essentially, the ant loses control over itself and is like a marionette puppet on strings. Ophiocordyceps effectively cut the ant’s limbs off from its brain and take their place, releasing chemicals that force the muscles there to contract. Essentially, the fungus uses mind control by releasing chemicals to control the Patient Zero’s nervous system. 

The fungus will eventually make up about half of Patient Zero’s entire body mass, completely hijacking the mind and body of the ant, rendering them a “zombie.” Patient Zero, however, is allowed to remain in the population, as the other ants are not yet aware of the fungal invasion.

Why would this fungus want to take over an ant? Just like the looming zombie apocalypse depicted in various forms of pop culture media, a zombie’s goal is to infect others and create more zombies—Ophiocordyceps wants just the same thing: to infect, spread, and grow. After several days, when Patient Zero is deceased and the internal fungus controls the bodily functions, it becomes time to infect others. The fungus guides the Patient Zero’s body to a leaf at a height of exactly 25 centimeters. This specific action baffled scientists, but they recently discovered that this is a microclimate zone with precisely the right humidity and temperature levels to promote Ophiocordyceps’ growth. The fungus forces Patient Zero’s body to permanently lock its mandibles around a leaf, so the ant’s body is hanging above a colony of vulnerable ants. Eventually, the fungus grows a long stalk directly through Patient Zero’s head. This rod grows a bulbous end that grows additional fungal cells. The hanging body acts as a launchpad for spores to disperse from, raining down on the ants below. Via this aerial attack, the other ants become infected and zombified. Rule 101 of zombies: make more zombies.

Ophiocordyceps Unilateralis is one of 28 species that infects ants, and there an estimated 1.5 million Ophiocordyceps species. Ophiocordyceps Unilateralis has been infecting this species of ants for the past 48 million years, based on fossil history. Beetles, spiders, and caterpillars have all been infected by Ophiocordyceps; who knows, one day there may be a species able to zombify humans. Or maybe, without us knowing, zombies already walk among us…