How Does the 'Zombie Ant' Fungus Work?

Some specialized fungi can hijack the behavior of ants, wasps, and spiders in order to spread their spores. Learn about the real-life Cordyceps and Ophiocordyceps fungi that inspired 'The Last of Us' in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/life/cellular-microscopic/zombie-ant-fungus.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff,
Lauren vogelbam here. Zombies are a horror trope for a reason.
For many reasons, really, but one is that we humans
tend to like the idea of being in control of
our own bodies and behavior, and in stories, the walking

(00:24):
dead are reduced to mindless doers of damage and often modernly,
spreaders of whatever infectious disease has caused the dead to rise.
There are many real life infections and conditions that can
alter a person's behavior, all horrific in their own right,
but none we know of could cause a full on

(00:46):
George Romero's style apocalypse or the Last of Us style apocalypse.
In the video games and television series The Last of Us,
a brain hijacking fungus evolves from the infecting insects and
other arthropods to infecting human beings. And don't worry, that's
the only spoiler we're going to give here. But today,

(01:06):
let's talk about the real life fungi that inspired the series.
Cordyceps and Afia. Cordyceps are each a genus of fungi
that are often parasitic to arthropods like ants, spiders, and wasps.
Fungi in general grow from spores, then consume living or
dead material like wood in order to grow root like

(01:29):
structures called mycelium and fruiting bodies like mushrooms that produce
more spores. But instead of in wood, Cortceps and Affia
cordyceps tend to grow in arthropods that in itself is
nothing very special. A fossil evidence of fungi growing in
insects has been found as far back as one hundred

(01:49):
and five million years ago, and over a thousand fungi
with insect hosts are known to exist today. But these
two genera of fungi can actually change an animal's behavior
when they're ready to spore in order to spread those
spores as far as possible. Take, for example, a species
of Apia cordyceps. The parasitizes carpent durants and hijacks the

(02:12):
ants behavior during the last days of its life. This
phenomenon caught the eye of British naturalist Alfred Russell Wallace
when he was in Indonesia back in eighteen fifty nine.
Even a newcomer to the area could see that something
was seriously wrong with some of the ants in the rainforest.
After all, carbondurants are generally pretty predictable in their behavior.

(02:35):
They work as a team, and each ant has a
very specific job, like building the nest, gathering food, or
caring for the queen. When an ant is infected with
the fungus, the fungus grows unnoticed in the ant's body
for a while, feeding on the ant until the fungal
cells account for over half of the ant's body mass.

(02:55):
All this time, the ant has been doing its usual
job and living its life. One day it begins to
act very differently. Breaking off from the colony. It stumbles
around by itself all day and night, climbing higher and
higher into the trees. Eventually, the ant clasps a leaf
for stem with its strong mandibles and dies. Check in

(03:19):
a week later, and you'll find the dead ant's body
covered in a brown mat of hair like structures, with
a beige stalk having erupted from a place near its head.
This stalk releases millions of tiny spores that float away
on the air for more ants to step on, thus
beginning the whole cycle over again. That chomping onto a

(03:43):
leaf for stem behavior by the way is how we
know that this kind of behavior altering fungal parasitism is
pretty ancient. Leaf scars created by an ant death grip
have been found on fossils at least forty eight million
years old. In all that time, carbenter ants have evolved
some strategies for avoiding these fungi, at least they try

(04:06):
their best. Many ant species groom each other in an
attempt to remove spores from their friends, while others fray
their nests with fungicidal poisons and seal off parts of
their nests. When infections arise, a whole ant colony will
relocate if necessary. But how does the fungus affect the

(04:26):
ants behavior to the extent that it does. It's a
question that's baffled generations of scientists over the years. Some
have argued that the ants aren't hijacked at all, that
certain protocols have evolved in response to a fungal infection,
and that the individual ants wander off not because they're
being influenced by the fungus, but to avoid infecting the
rest of their colony. And despite the tropes about zombies

(04:50):
and brains, a twenty seventeen study published in the Proceedings
of the National Academy of Sciences found that it's possible
that the ant's brain isn't involved in the whole process
at all. The researchers found that as the fungus grows
inside the ant's body, its cells create an interconnected network
of fibers that surround the ants muscle fibers, and that

(05:12):
it's this network that is most likely coordinating the ants movements.
They did find the fungus in the insect's head, but
not in its actual brain. In a press release, the
lead author of the study, an entomologist by the name
of David Hughes, said, we found that a high percentage
of the cells in a host were fungal cells. In essence,

(05:34):
these manipulated animals were a fungus in ants clothing. Pretty
much everything except the brain had been taken over entirely
by fungal cells, which led the researchers to believe that
the fungus might be preserving the brain for a reason,
maybe in order to help the ants survive until it
can perform its final death bite. To be fair, ant's

(05:57):
brains are pretty small, and they make up for that
by having clusters of neurons throughout their bodies that help
control different work, like the movement of a pair of
legs or receiving signals from an antenna. So although these
findings are compelling, it's still not crystal clear what's going
on between these parasitic fungi and their victims. But at

(06:20):
least it is clear that it would be extremely difficult
for a fungus to start hijacking human bodies in the
way that cordyceps and a few cordyceps do with arthropods,
so that's one less thing to worry about. Today's episode
is based on the article Meet the Zombie ant Fungus
that inspired HBO's The Last of Us on how Stuffworks

(06:43):
dot com, written by Jeslin Shields. Brain Stuff is production
of iHeartRadio in partnership with how Stuffworks dot Com and
is produced by Tyler Klang. Four more podcasts my Heart Radio,
visit the iHeartRadio app, Apple Podcasts, or wherever you listen
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