The Zombie Fungus from The Last of Us Is Real. Here's What It Actually Does.
Photo coming soon
The game got the mechanism right. It got almost everything else wrong. Here is what Ophiocordyceps actually does — and why Japan has been using its relatives for a thousand years.
When The Last of Us premiered, the question that spread through gaming and television communities was: is the zombie fungus real?
The answer is yes. Sort of.
There is a real fungal parasite that infects insects, hijacks their behavior, steers them to a specific location, and then kills them to spread its spores. The organism is Ophiocordyceps unilateralis. It has been doing this for at least 48 million years — fossil leaf impressions from the Messel Formation in Germany preserve the characteristic bite-mark scars on leaf veins consistent with manipulated ant behavior, long before humans evolved.
The game designers knew the biology. The fungus in The Last of Us is explicitly based on Cordyceps research, and the show's opening minutes include a scientist explaining the real mechanism.
What the game invented: a version that can infect humans, spread through breathing, and survive at mammalian body temperature.
What actually limits Ophiocordyceps to insects is more interesting than the fiction.
How the Zombie Ant Fungus Actually Works
Ophiocordyceps unilateralis is an entomopathogenic fungus — a parasite of insects. Its primary hosts are carpenter ants of the genus Camponotus, primarily in tropical and subtropical forests.
The infection begins when a spore lands on an ant and penetrates the cuticle. The fungus does not invade the ant's brain, despite how the process is usually described. Recent research using 3D imaging has shown that the fungal cells colonize the ant's muscles throughout the body — particularly the muscles controlling the mandibles — while largely avoiding the brain itself.
The behavioral manipulation comes through chemical interference. The fungus produces compounds that disrupt the ant's normal chemical communication and muscle control. The infected ant leaves the colony (which would normally respond to sick members by removing them), climbs upward on vegetation, bites down on a leaf vein with its mandibles, locks its jaw muscles in a grip it cannot release, and dies in position.
The height, location, and timing of this death are not random. O. unilateralis steers the ant to a specific microhabitat — a particular height above the forest floor, a particular humidity range, a particular light exposure — that is optimal for the fungus's next stage. After the ant dies, the fungal stalk grows from the ant's head, producing a fruiting body that releases spores downward onto the foraging trails of healthy ants below.
The precision of this manipulation — the fungus moving an animal to a specific GPS coordinate, so to speak, to optimize its own reproduction — is one of the more remarkable examples of parasite behavior modification in nature.
Why It Can't Infect Humans
The question that follows the "is it real?" question is always: could it evolve to infect us?
The short answer is: not plausibly in any timeframe that should concern you.
Three barriers separate Ophiocordyceps from human hosts:
Body temperature: Humans maintain a core temperature of approximately 37°C. Most Ophiocordyceps species thrive in the temperature range of 20–30°C — the ambient temperatures of the tropical forest floor. The warm-bodied immune systems of mammals have co-evolved with fungi for millions of years precisely because elevated temperature creates an inhospitable environment for fungal growth. This is why fungi rarely cause serious disease in healthy humans but can be devastating in immunocompromised patients whose defenses are impaired.
Immune system complexity: The mammalian immune system has multiple overlapping defenses against fungal invasion — physical barriers, innate immune cells, adaptive immune responses — that insects largely lack. A fungus that has evolved to exploit ant biology faces an entirely different immune landscape in a mammal.
Biochemical specificity: The compounds Ophiocordyceps uses to manipulate ant muscle function are specific to the biochemistry of Camponotus ants. They work because the fungus has co-evolved with these particular hosts over tens of millions of years, fine-tuning its chemical toolkit to match the specific receptor profiles and neurochemical pathways of its target. Human biochemistry is different in fundamental ways.
For Ophiocordyceps to infect humans, it would need to simultaneously solve all three problems — and do so while under evolutionary pressure from multiple competing organisms in an environment it currently cannot survive. The probability is not zero, but it is vanishingly small.
The fungal diseases that actually threaten humans — Candida auris, Aspergillus fumigatus, Cryptococcus neoformans — come from organisms that are already adapted to warm environments, already generalist pathogens, and already present in human environments. If you want to worry about fungal disease, those are the ones worth following.
Japan's Cordyceps: Tochukaso and a Different Tradition
Here is where the Western narrative around Cordyceps typically stops: zombie ants, can't infect humans, fascinating biology, see you next time.
What it misses is that Japan has its own deep relationship with Cordyceps-related fungi — a relationship that is not about horror but about medicine.
Tochukaso (冬虫夏草, literally "winter worm, summer grass") is the Japanese name for Cordyceps species that parasitize caterpillars and other insects in mountain regions. The name captures the observed phenomenon: in winter, a worm; in summer, what grows from it looks like grass. The fungal stalk emerging from the mummified insect was interpreted — correctly — as a single organism whose visible form changes with the season.
Japan's engagement with tochukaso goes back at least to the Edo period, when it appears in pharmacological texts as a tonic for fatigue, respiratory weakness, and recovery from illness. The tradition came to Japan from Chinese medicine (dongchong xiacao in Mandarin), where it had been recorded since at least the 15th century.
The traditional preparation: dried tochukaso was simmered in broth or steeped in sake, with the liquid consumed as a tonic. The insect body and fungal stalk were both used. Mountain practitioners in regions where the fungus was found — high-altitude meadows and forest edges — collected it seasonally, at considerable effort, which contributed to its high value.
This is categorically different from the zombie ant dynamic. The insects parasitized by tochukaso species do die, but the behavioral manipulation is less dramatic than O. unilateralis — the caterpillar host is typically already underground or in a protected position when infection takes hold, rather than being steered to a specific location. The ecology is different; the traditional use is different; the cultural meaning is different.
What connects them is the phylum: Ascomycota, the same major fungal group, adapted to entirely different ecological niches.
But Japan also has its own zombie ant fungus.
Ophiocordyceps camponoti-japonici — identified in specimens from Kanto and Tokai region forests — is the Japanese equivalent of O. unilateralis. It parasitizes Japanese carpenter ants (Camponotus japonicus and related species), manipulating their behavior in the same way as its tropical relatives: the infected ant leaves the colony, climbs vegetation, bites onto a surface, and dies in position while the fungus completes its cycle.
O. camponoti-japonici does not inhabit the alpine meadows where tochukaso is found. It is a forest floor organism, operating in the broadleaf and mixed forests of central Japan. Most forest walkers will never see it; the infection is localized and the fruiting bodies are small. But it is there.
The two lineages of Japanese Cordyceps — the medicinal tochukaso of the mountain pharmacopeia and the zombie-ant specialist in the forest understory — coexist in the same country without overlap, doing entirely different things with the same basic biological toolkit.
The Science Behind the Traditional Claims
The compound that has received the most research attention from tochukaso and its cultivated relatives is cordycepin (3'-deoxyadenosine). This adenosine analog was first isolated from Cordyceps militaris — a species that parasitizes moth pupae and is now commercially cultivated — in the 1950s.
Laboratory research has shown cordycepin to have interesting properties: it interferes with RNA synthesis in ways that have shown antiproliferative effects in cell culture studies. Research has also examined cordycepin's effects on inflammation pathways and energy metabolism.
The important caveat: most of this research is in vitro (cell culture) or animal models. Human clinical evidence for cordycepin-specific effects is limited. What exists is primarily for Cordyceps sinensis and Cordyceps militaris extracts, not isolated cordycepin, and the studies vary considerably in quality and design.
What is established in human research: a 2010 randomized controlled trial published in the Journal of Alternative and Complementary Medicine (Xu et al.) found that Cordyceps sinensis supplementation improved exercise performance in older adults at altitude. Athletic performance enhancement claims in supplement marketing typically trace back to the Chinese national athletic team's 1993 performances at the World Championships — performances that were attributed to cordyceps supplementation by the team's coaches, though the specific attribution was contested.
The traditional claims — energy, endurance, respiratory support — have some scientific backing, but the quality of evidence is weaker than the supplement industry's presentation suggests. Research suggests plausible mechanisms. It does not prove the effects claimed on most product labels.
The Taxonomy Correction No One Told You About
A note on naming that matters for anyone following the science: in 2007, a phylogenetic study reorganized the Cordyceps genus significantly.
What was previously called Cordyceps unilateralis (the zombie ant fungus) was reclassified as Ophiocordyceps unilateralis. Many other species moved from Cordyceps to Ophiocordyceps and related genera. The commercially important Cordyceps sinensis (the traditional tochukaso species used in Chinese and Japanese medicine) was reclassified as Ophiocordyceps sinensis.
The species most commonly cultivated for supplements — Cordyceps militaris — retained its name, as it was determined to belong to the original Cordyceps lineage.
This matters because:
When you see "Cordyceps" on a supplement label, you are usually getting C. militaris — the easiest species to cultivate at scale, with a reasonable compound profile, but not the same organism as the Himalayan O. sinensis that the traditional reputation was built on.
After the Rain
The zombie fungus narrative — compelling, cinematic, accurate about the mechanism — has done something useful for public understanding of fungi: it has made the idea of interspecies chemical communication viscerally comprehensible. Most people now have an intuitive grasp of the mycorrhizal network because they've seen the concept in Avatar. Most people now have an intuitive grasp of fungal behavioral manipulation because they've seen The Last of Us.
This is good. The mechanism is real, the biology is stranger than the fiction needs to be, and the jump from "insects can be hijacked by fungi" to "fungi shape ecosystems and have been shaping them for hundreds of millions of years" is a short one.
Japan's tochukaso tradition understood something different about the same organism type: that the fungus is not only terrifying. It can be ally as well as predator, depending on whose perspective you're taking.
After the rain, the mushrooms appear. Some of them have been doing stranger things than the game imagined.
AfterRain is named for the moment when something that was always there becomes visible.
A note on tochukaso: Wild Ophiocordyceps sinensis collection in Japan requires specialist knowledge of high-altitude habitats and specific host insects. It is not a casual foraging activity. Commercial Cordyceps militaris is widely available cultivated; this is the species in most supplements.
References
Tags: cordyceps real life, last of us fungus real, zombie fungus Japan, ophiocordyceps unilateralis, tochukaso Japan, cordyceps mushroom, zombie ant fungus, Japanese medicinal fungi, cordyceps supplement truth, AfterRain
Topics