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 usually don’t count.
But a new program on HBO, called The last of the Us, presents a compelling case that there might be such a thing as a realistic zombie. Or realistically. And it’s definitely scary.
The premise of the show, which is based on the popular video game of the same name, isn’t too different from your typical post-apocalyptic horror story: American cities are crumbling, there are rabid people everywhere, and a manly man must protect a young girl as they travel across the whole country.
The zombies, however, are truly inspired. More specifically, they are inspired by nature – by real zombies living on Earth.
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 mushroom is real.
In tropical, subtropical and even temperate forests around the world, there are many species of fungi in the genera Cordyceps and Ophiocordyceps (these fungi were previously just called Cordyceps) that infect insects such as ants and other invertebrates. And they basically turn them into zombies. The fungi take over their minds and bodies, causing them to behave in such a way that they spread spores to others of their kind.
The mushrooms were popularized in 2016 by the show Planet Earth, who caught an Ophiocordyceps parasitizing a bullet ant. And it was actually the clip below – where the fungus makes the ant climb a branch, before killing it and sprouting a spore-producing fungus from the ant’s head – that inspired the game’s creator, Neil Druckmann.
So, the fungus is real, and it can turn insects into zombies. It’s pretty cool. But does it pose a threat to us?
A comforting fact is that people have been eating Cordyceps for centuries now without going rabid. It is a traditional Chinese medicine used to treat kidney disease and other ailments. Even wellness brands are now promoting it.
But to be sure – because you really can’t be sure enough, can you? — I contacted Charissa de Bekker, a mycologist who researches Ophiocordyceps. De Bekker, who is a professor of biology at the University of Utrecht in the Netherlands, has not seen the show, but is familiar with the game. Our conversation has been edited for length and clarity.
To be clear, the mushroom in the show The last of us is real, right?
Yes. Cordyceps and Ophiocordyceps fungi are real and infect insects in nature. There are many different species out there.
Many!? How many?
Scientists have described at least 30 Ophiocordyceps species that parasitize ants, but we know there are many more, because each ant species that becomes infected has its own specialized Ophiocordyceps species.
There are also Ophiocordyceps and Cordyceps fungi that infect other insects such as wasps and flies. We also see that this goes beyond insects to arthropods such as spiders. Then there is a completely different group of fungi, in the order Entomophthorales, that also perform manipulation – and these species look nothing like Ophiocordyceps.
Manipulation has evolved several times throughout the mushroom kingdom. The biodiversity of these fungi is probably very high, we just haven’t discovered them all yet.
How do these fungi manipulate their hosts in nature?
What we see, especially with ants, is that they pick up spores [which are kind of like seeds for fungus] when they go out to search for food. The spore infects the ant and fungal cells begin to grow inside the body.
At first, this ant may behave normally. But eventually it stops participating in the colony’s attempts. It communicates poorly with its nestmates anymore.
And then this ant starts to become hyperactive and no longer has the same daily rhythms as the other ants. Most carpenter ants, for example, forage at night, but the infected ant basically becomes active all the time.
At some point, the infected ant wanders away from the colony to find a place in the forest to climb and bite [down on the twig or vine]. This is where the fungus will quickly begin to consume everything inside, killing the host. The fungus uses that energy to germinate a population with a fruiting body — the fungus, if you will — that has spores that will fly out and infect more ants.
By climbing higher in the forest, the ant basically helps the fungus spread its spores. The specific place it chooses to climb can actually aid in the development of the fungus.
This whole process can take days or weeks, or even months. What you often see in zombie movies, or The last of us, things happen much faster. In nature, things take some time.
Is Ophiocordyceps actually controlling the ant’s mind?
We think this fungus secretes certain chemicals that can bind to or interact with receptors or other types of proteins that are related to the nervous system, and that normally give rise to different behaviors. For example, these could be receptors that would normally bind to dopamine or serotonin, which could then induce a certain type of behaviour. We are still very much in the process of trying to figure it out.
We certainly think it’s more than just this fungus gnawing away at some brain tissue because the behavior is so specific.
Would you call these infected hosts “zombies”? Is it scientifically accurate?
If you compare it one-on-one with pop culture zombies, it’s not exactly accurate. These insects are very much alive, while in fictional films zombies are often undead. These ants infected with Ophiocordyceps are not dead and are walking around.
What makes real hosts similar to fictional zombies is that they behave in such a way that they benefit the parasite, not the host.
Is there any reason to believe that such a fungus 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, nervous tissue and body temperature. Even if the fungi were able to cause a small infection, the machinery needed for the fungus to perform such precise manipulation is simply not there.
These fungi developed strategies to manipulate specific insect hosts over millions and millions of years. They are not generalists. Each species only knows how to deal with one particular insect.
We don’t see the mushroom specialists just jumping from one species of ant to another, let alone from one species of ant to another insect. Spreading from ant to human is just such a big jump.
In the show, a fictional epidemiologist suggests that climate change may make harmful fungi more tolerant of warmer temperatures. As a result, they could more easily jump to warm-blooded humans. Is that a real concern?
Indeed, it is a real concern that medical mycologists have [about harmful fungi like Candida auris, not Cordyceps]although that is not my expertise.
Most fungal infections are skin infections – or if you’re an immunocompromised patient, for example, certain spores that are normally benign can lodge in your lungs and cause a problem. But most fungi do not grow happily at our body temperature. Most of them actually prefer lower temperatures.
Some experiments show that fungi may be able to adapt to higher temperatures as they adapt to a warmer world. You can imagine that if their optimal temperature gets closer to our body temperature, yeast 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 fungus-infected zombies were real, right?
If you play the game, you will see that spores play a role in spreading infection. But no, the fungus would not spread through biting. In general, across the fungal kingdom, going from one place to another, or from one host to another, occurs by spores.
I’m a big fan of mushrooms. They break down plants, they can be psychedelic. They are also delicious. Is it unfair that Cordyceps is the villain of the series?
It’s great that finally mushrooms are hip and happening. I hope the show sparks interest in fungi in general, because they are incredibly fascinating organisms. They are more important than people might think.
They’re very much the villain of the show, and that’s generally how we see parasites, because they make us sick. But in nature they are actually super important and just as important as all other organisms.
They keep everything in check. If ants, for example, were not bothered by certain parasites – not just Ophiocordyceps, but anything else that makes them sick – then their numbers could get out of control. You can get an overpopulation of certain species. Taking out a parasite like this fungus can be like taking out a predator from the ecosystem, and it can lead to a reduction in biodiversity.
I’m a little afraid to ask, but how common are mushrooms in general?
Not to scare you, but in every breath of air you take there will be fungal spores. Most of them aren’t harmful to us – most of the spores you inhale right now are benign, or fungi that don’t know how to deal with our bodies, so you’ll never notice them. But they are everywhere.