The “zombie” fungus in The Last of Us, explained by a biologist

A new HBO show, The Last of Us, is about a fungi-fueled apocalypse. Above, lead characters Joel (Pedro Pascal) and Tess (Anna Torv) discover a human body that was taken over by a fungus. | Liane Hentscher/HBO

The good news: You’re safe if you’re not an ant.

The scariest shows and movies are often the ones rooted in reality — about psychopathic serial killers, late-night home invasions, and AI robot dolls. Zombie apocalypses typically don’t count.

But a new show on HBO, called The Last of Us, presents a compelling case that perhaps there’s such a thing as a realistic zombie. Or realistic-ish. And it’s definitely scary.

The premise of the show, which is based on the popular video game of the same name, isn’t that different from your typical post-apocalyptic horror story: US cities are crumbling, there are rabid humans everywhere, and a manly man has to protect a young girl as they travel across the country.

The zombies, however, are truly inspired. More specifically, they are inspired by nature — by real zombies that live on Earth.

Liane Hentscher/HBO

Pedro Pascal, of The Mandalorian and Narcos, stars in HBO’s The Last of US as Joel Miller, the lead protagonist.

In the show, which premiered last Sunday, it’s not a virus that turns people into brainless automatons but a kind of fungus called Cordyceps. The fungus takes over their minds and bodies and makes them want to spread the fungus to the uninfected.

This fungus is real.

In tropical, subtropical, and even temperate forests around the world, there are many species of fungus in the genuses Cordyceps and Ophiocordyceps (these fungi were formerly called just Cordyceps) that infect insects like ants and other invertebrates. And they do essentially turn them into zombies. The fungi take over their minds and bodies, causing them to behave in such a way as to spread spores to others of their kind.

The fungi were popularized in 2016 by the show Planet Earth, which captured an Ophiocordyceps parasitizing a bullet ant. And it was actually the clip below — in which the fungus causes the ant to climb up a branch, before killing it and sprouting a spore-producing mushroom from the ant’s head — that inspired the game’s creator, Neil Druckmann.

So, the fungus is real and it can turn bugs into zombies. That’s pretty rad. But does it pose a threat to us?

A comforting fact is that people have been eating Cordyceps for centuries now without turning rabid. It’s a traditional Chinese medicine, used to treat kidney disease and other ailments. Even wellness brands are now marketing it.

But to be sure — because one really can’t be sure enough, right? — I reached out to Charissa de Bekker, a mycologist who researches Ophiocordyceps. A professor of biology at Utrecht University in the Netherlands, de Bekker has not seen the show but is familiar with the game. Our conversation has been edited for length and clarity.

To be clear, the fungus in the show The Last of Us is real, right?

Yes. Cordyceps and Ophiocordyceps fungi are real and infect insects in the wild. There are many different species out there.

Many!? How many?

Researchers have described at least 30 Ophiocordyceps species that parasitize ants, but we know there are many more, because every ant species that gets infected has its own specialized Ophiocordyceps species.

There are also Ophiocordyceps and Cordyceps fungi that infect other insects like wasps and flies. We also see this go beyond insects to arthropods like spiders. Then there’s a whole other group of fungi, in the order Entomophthorales, that does manipulation as well — and these species don’t look anything like Ophiocordyceps.

Manipulation has evolved multiple times across the fungi kingdom. The biodiversity of these fungi is probably really high, we just haven’t discovered them all yet.

Kevin Wells/Getty Images

A type of Cordyceps fungus growing on a bullet ant near Puerto Viejo de Sarapiqui, Costa Rica.

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Another kind of “zombie” fungus grows out of a dead winged insect in a rainforest in Vietnam.

How do these fungi manipulate their hosts in the wild?

What we see, specifically with ants, is that they pick up spores [which are kind of like seeds for fungus] when they go out to forage for food. The spore infects the ant and fungal cells start growing inside its body.

In the beginning, this ant might act normally. But eventually, it stops participating in the foraging efforts of the colony. It doesn’t communicate well with its nest-mates anymore.

And then this ant starts to become hyperactive and no longer has the same daily rhythms of the other ants. Most carpenter ants, for example, forage during the nighttime, but the infected ant basically becomes active all the time.

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A “zombie” fungus sprouts a fruiting body (mushroom) out of an ant in Indonesia.

At one point, the infected ant wanders off from the colony to find a spot in the forest to climb and bite [down on the twig or vine]. This is where the fungus will quickly start to consume everything inside, which kills the host. The fungus uses that energy to sprout a stock with a fruiting body — the mushroom, if you will — which has spores that will fly out and infect more ants.

By climbing higher up in the forest, the ant basically helps the fungus spread its spores. The specific spot it chooses to climb may actually help with the development of the fungus.

This whole process could take days or weeks, or even months. What you often see in zombie movies, or The Last of Us, things happen a lot quicker. In nature, things take some time.

Are Ophiocordyceps actually controlling the minds of ants?

We think this fungus is secreting certain chemicals that can bind to or interact with receptors or other sorts of proteins that are related to the nervous system, and normally give rise to different behaviors. For instance, these could be receptors that normally would bind to dopamine or serotonin, that might then elicit a certain type of behavior. We’re still very much in the process of trying to figure that out.

We certainly think it’s more than just this fungus gnawing away on some brain tissue because the behavior is so specific.

Liane Hentscher/HBO

A zombie is plastered to the wall by the Cordyceps fungus in Episode 1 of The Last of Us.

Would you call these infected hosts “zombies”? Is that scientifically accurate?

If you compare it one-to-one with zombies from pop culture, it’s not completely accurate. These insects are very much alive, whereas in fictional movies zombies are often undead. These ants infected with Ophiocordyceps are not dead and walking around.

What makes real-life hosts similar to fictional zombies is that they are behaving in such a way as to benefit the parasite, not the host.

Is there any reason to believe that a fungus like this could infect a human body and turn us into zombies?

The very short answer is: No.

Everything in the human body is so different from the insects that these fungi normally infect, including our physiology, our nervous tissue, and our body temperature. Even if the fungi were able to cause a small infection, the machinery that is needed for the fungus to do such a precise manipulation is simply not there.

These fungi evolved strategies to manipulate specific insect hosts over millions and millions of years. They’re not generalists. Each species only knows how to deal with one particular insect.

We don’t see the fungi specialists just jumping from one ant species to another, let alone from an ant species to another insect. Spreading from ant to human is just such a big jump.

In the show, a fictional epidemiologist suggests that climate change could make harmful fungi more tolerant to warmer temperatures. As a result, they could more readily jump to warm-blooded humans. Is that a real concern?

That’s actually a real concern that medical mycologists have [about harmful fungi like Candida auris, not Cordyceps], though that’s not my expertise.

Most fungal infections are skin infections — or if, say, you’re an immunocompromised patient, certain spores that normally are benign might settle in your lungs and cause a problem. But most fungi don’t happily grow at our body temperature. Most of them actually prefer lower temperatures.

Some experimentation shows that fungi could, perhaps, adapt to higher temperatures, as they adapt to a warming world. You can imagine that if their optimal temperature comes closer to our body temperature, fungal infections could become more of a problem.

In the show, the fungus spreads through bites, not spores. That’s not how it would actually work if these fungi-infected zombies were real, right?

If you play the game, you’ll see that spores do play a role in spreading infection. But no, the fungus wouldn’t spread through biting. Generally, across the fungal kingdom, going from one spot to another, or from one host to another, is done by spores.

I’m a big fan of fungi. They decompose plants, they can be psychedelic. They’re also delicious. Is it unfair that Cordyceps are the villain in the show?

It’s great that, finally, fungi are hip and happening. I hope the show sparks some interest in fungi in general, because they’re incredibly fascinating organisms. They’re more important than people might think.

Luis Espin/Getty Images

A Cordyceps fungus grows out of a wingless insect on a leaf in Ecuador.

They are very much the villain in the show, and that’s generally how we see parasites, because they make us sick. But in nature, they’re actually super important and just as important as all the other organisms.

They keep everything in check. If ants, for instance, weren’t pestered by certain parasites — not just Ophiocordyceps but anything else that makes them sick — then their numbers might get out of control. You might get an overpopulation of certain species. Taking out a parasite like this fungus might be like taking out a predator from the ecosystem, and that could cause biodiversity to decline.

I’m kind of afraid to ask, but how common are fungi, in general?

Not to scare you, but in every breath of air you take there will be fungal spores. Most of them are not harmful to us — most spores you’re inhaling right now are benign, or fungi that don’t know how to deal with our body, so you will never even notice them. But they are everywhere.