A fungus that hijacks insects inspired one of the scariest ideas in science fiction

A parasitic fungus that turns ants into puppets has quietly become one of the most influential organisms in modern pop culture, inspiring a video game, an HBO series, and a wave of fascinated dread about what a mutated version might do to something bigger than an insect. The real organism behind it all, Ophiocordyceps unilateralis, does not need to touch a human to be unsettling; its documented effects on carpenter ants are disturbing enough on their own.

The Real Biology Behind a Cordyceps Takeover

The fungus infects carpenter ant workers and compels them to leave the safety of the colony, climb vegetation, and clamp their mandibles into the underside of a leaf or twig in a behavior researchers call summiting. According to a Penn State-led study published in the Proceedings of the National Academy of Sciences, the fungus surrounds and invades muscle fibers throughout nearly the ant’s entire body, forming a three-dimensional network of connected fungal cells that appears able to coordinate the host’s movements collectively. Once the ant is locked in place, the fungus consumes it from the inside and sprouts a stalk from its head that releases spores onto the ground below, continuing the infection cycle among ants that forage nearby.

Control From Outside the Brain

What makes the mechanism especially strange is what the fungus does not do. Using serial block-face scanning-electron microscopy and machine-learning image analysis developed with University of Notre Dame collaborators, the Penn State team found fungal cells throughout the ant’s head, thorax, abdomen, and legs, but none inside the brain itself. Senior author David Hughes, an entomologist at Penn State, described the effect as a parasite operating “almost like a puppeteer pulls the strings to make a marionette move,” controlling the ant’s muscles directly rather than issuing commands through the nervous system’s normal chain of command. Hughes, who also consulted on the video game that dramatized this biology, told Northeastern Global News that the fungus pushes chemical compounds across the ant’s blood-brain barrier rather than physically invading the brain, allowing it to influence behavior “at a distance” while apparently preserving enough brain function to keep the host alive until the fatal bite is locked in.

A Dome of Death Above the Colony

The fungus’s strategy is also a response to ant society’s own defenses. Colonies are generally good at detecting sick nestmates through changes in scent and chemistry, and an infected ant would normally be carried out and discarded before it could spread spores nearby. To get around that, Hughes told Northeastern, the parasite drives its host to wander off and die outside the colony on its own, positioning the corpse directly over the foraging trails other ants use daily. “The ants are forced every day to go out looking for food, so as they go out, they walk underneath a sniper’s alley of their dead siblings,” Hughes said, describing the resulting cluster of spore-releasing cadavers as “a dome of death” that surrounds active colonies and helps explain why the fungus keeps winning against its host’s collective defenses.

From a Nature Documentary to a Zombie Franchise

That biology reached a mass audience by way of television rather than a biology textbook. Neil Druckmann, creative director of the 2013 video game “The Last of Us,” has said the concept came directly from watching a BBC “Planet Earth” segment on the cordyceps fungus, telling NPR at the time that the idea of a mind still present while something else controls the body struck him as an especially unsettling fate. The game, and the HBO series it later spawned, reimagined a mutated strain of the fungus jumping from insects to humans and producing infected “runners” and “clickers” whose twitching, hyperaggressive early symptoms echo the real convulsions cordyceps triggers in ants before summiting behavior sets in.

Why the Jump to Humans Remains Fiction

Entomologists who study the fungus are consistent on one point: the underlying biology does not translate to people. Hughes and Northeastern-based biologist Rebeca Rosengaus have both said the motor systems of ants and humans are different enough, evolutionarily, that Ophiocordyceps unilateralis has no plausible path to infecting a human nervous system the way it does an insect’s. San Diego Natural History Museum entomologist Michael Wall made a similar point to NPR back in 2013, noting that insects have long inspired science-fiction writers precisely because parasitic behavior control is common in that world and essentially unheard of in vertebrates. The fungus remains, in other words, a genuinely documented piece of biology that happens to make an ideal source of fictional horror rather than a realistic public health threat, which is part of why it has proven such durable material for storytellers who found the real thing frightening enough without embellishment.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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