Real-life zombies

Support for Unexplainable comes from Anthropic, the team behind Claude.

You know those questions that keep you up at night?

The ones that make you fall down rabbit holes until 2 a.m.

Claude is an AI that can help you if you want to dive deeper.

Instead of rushing to surface-level answers, you can use Claude to help work through the complexity.

You can upload documents, you can search the web, and you can explore different angles on problems that genuinely interest you.

You can try Claude for free at claude.ai/slash unexplainable.

Before we start the show, I want to tell you about a new way to listen to Unexplainable by becoming a Vox member.

You'll get access to a new feed where you can listen ad-free, just a steady stream of science mysteries with no breaks.

You'll also be able to read every article on Vox.com.

You get access to a member exclusive newsletter, and you'll get a whole bunch of other perks.

More importantly, though, you'll be supporting Unexplainable.

Making this show, diving into these unanswered questions, it takes a lot of time and effort and drafts.

So many drafts.

And every new Vox member gives us a stable base of support that allows us to make even more ambitious episodes and long-term series.

We truly can't make this show without you.

And right now, Vox is offering 30% off an annual membership.

All you have to do is go to Vox.com/slash members to join.

Thanks.

All right, so

we're going to fade up on a moonlit field.

You can see tall grasses moving in the breeze, a little bit of moonlight, and you can see on one of the blades of grass, there's an insect with its wings spread wide.

This is Mindy Weisberger, a science writer.

It looks like it might be a bee because it seems to be striped with bands of yellow and black.

But you get a little closer and you see that it is not a bee.

It is in fact a fly.

It is a dead fly.

And the yellow bands that are striping its body are actually a fungus that has grown inside it and then burst through the seams in its exoskeleton.

How did this fly become the star of a real-life horror movie?

Well, several days ago, a spore from a fungus landed on it, and the spore buried inside of the fly.

and then started extending little filaments throughout its body, these fungal tendrils, essentially, that started digesting the fly from the inside out, consuming its fat cells.

Now, the fly, as this was happening, behaved pretty normally, at least at first.

But over the next few days, the fungus continued to grow, and it started congregating its cells first around the fly's heart, and then around what is the spinal cord in insects, and then around its brain.

And then, after it had pretty much consumed most of the fat reserves in this fly, it was ready for the next stage, reproduction.

So this is where the fly stops behaving like a fly and starts behaving like a fungus in a fly suit.

It finds a place where it can climb, and it's thought that Getting to a higher position is better for the fungus because it produces these spores that are released in kind of an explosive poof.

And the higher they are, the more widely they are likely to disperse.

So the infected fly climbs up a blade of grass until it is literally no longer able to walk anymore.

Again, stuffed with fungus.

So at a certain point, it stops walking.

It extends its proboscis, which is a little trunk-like mouth part, and oozes out a sticky substance to basically glue it into place.

And then the fly dies.

Its abdomen cracks open, and the spores come spilling out, ready to land on new flies and infect them.

And to increase the odds that a fly will get spored, the fungus turns into a kind of horrible fly fatale.

These dead

fungus-striped flies with their big bloated abdomens are very attractive to male flies who are looking to mate.

Apparently, male flies of this species find big swollen abdomens very alluring.

And they also find this scent that the fungus tries to pump out, this chemical signal, alluring too, like a

sexy fungal love perfume.

That also sends a signal to male flies like, hey, you know, maybe here's something that you want to, you know, you want to hit that.

I'm sorry.

All of this draws in new victims who, if everything works out, will soon be turned into their own fungal fly puppets.

Now, Mindy has a word for this kind of horror story, zombification.

She calls these flies real-life zombies.

And the fungus that takes them over is a real-life zombifire.

And it turns out, there are a lot of examples of zombies and zombifiers out in nature.

There are so many, in fact, that Mindy wound up writing a whole book about them called Rise of the Zombie Bugs.

So, this is Unexplainable.

I'm Bert Pinkerton.

And today on the show, Mindy will tell us what we know and what we don't know about

zombie bugs.

Okay, let's start by just defining some terms.

What do we mean when we say like zombifier or zombie?

Sure.

So a zombifier is an organism that manipulates the behavior of its host.

And a zombie is an organism that is being manipulated to behave in a way that it normally would not, and which only benefits the parasite that's manipulating it.

So to a certain extent, like let's say you catch a cold,

you're going to change your behavior because you're feeling sick.

You feel like you need to rest more, you need to drink more water.

These are all things that help you fight off the infection.

So in a certain certain sense, that's the cold virus generating a change in behavior, but it's a behavioral change that actually benefits you.

For a zombie, the changes to its behavior are not something that benefit the host, they only benefit the parasite.

That's what makes it a zombie.

So, it'd be like if I got sick and instead of going into my room and trying to sleep it off, I went and I licked everybody that I could lick in order to spread the cold virus.

Exactly.

And so, there are zombifying viruses.

There are zombifying fungi.

There are insects that are able to zombify their hosts.

There are worms that can zombify their hosts.

So

most

of the organisms that they infect are arthropods.

So bugs, but the colloquial version of bugs.

Bugs.

Exactly.

I do have to apologize to entomologists because as far as entomologists are concerned, bugs are only insects with sucking mouth parts.

However, as we all know, colloquially, bugs cover

a much broader range.

Poor entomologists.

Do you have personal favorite thomifiers or ones that make you squirm?

Let's see.

So, hairworms infect terrestrial insects, but hairworms reproduce in water.

And

let's say a cricket is infected by a hair worm.

Now, the worm grows inside this cricket.

It grows to the point where it is many times the length of the cricket itself.

Like to the point where if you look at a cricket that is infected, you might be able to see it moving around the abdomen.

This actually spoke to me because when I was pregnant, during the last month of my pregnancy, the fetus is getting really big at this point.

So, you know, it's kind of like the movie Alien, right?

Like you could see the foot, you could see an elbow.

It's like, you know, there's something, there's, there's something alive moving around inside your body.

That is actually kind of what these infected crickets look like.

But the worm has to get out eventually.

So what it does is it manipulates the cricket's behavior to get it to find water and then jump in.

And once it's in the water, the worm starts to emerge.

So watching a cricket trying to swim in a pool of water while this long thread-like worm is slowly over minutes spooling out from its backside

is something I highly recommend watching if you really want to squeak yourself out.

Oh my god, it's like, oh,

sick.

There are many, many videos of this on YouTube.

That is so friggin nasty.

This is so gross.

Tyler's getting exhausted.

This is so gross.

Oh,

okay.

But so

there are all these different approaches, you're telling me, that fungi and viruses and insects use to to do this zombifying

what are the what are the sort of biggest categories of mysteries i guess about about how they do this

okay

some of the biggest mysteries start with the moment that the host is infected because obviously a body's first response to any kind of infection is going to be an immune response.

So the first thing that a zombifier needs to do is to somehow get past that.

And so that's a big, that's a big question is for zombifiers from viruses to wasps to fungi to worms, when they get inside an organism where they're not supposed to be, how exactly are they telling their host's immune system, No, there's nothing to see here.

You can just go about your business.

You don't need to worry about me.

So that's that's mystery number one.

Yeah, that's a big one.

Then, of course, another one is once it gets to the point of manipulation, first of all,

what are the cues?

How does it decide, okay, now is the right time to get this host moving to a place where I need to be?

So the description that I gave you earlier of the

fly in a moonlit field, there seems to be a circadian rhythm element to the fungus that infects flies specifically because they start their climbing at night.

Got it.

So mystery number two would basically be,

are there things out in the environment that trigger a fungal takeover?

And how does the zombifier kind of recognize those cues, I guess, it sounds like.

Yeah.

And the third big question is obviously the nuts and bolts of how is it manipulating behavior?

Right.

The thing about this field is that there is still so much that scientists are piecing together about the precise mechanisms of how this works.

Behavior is something that is just super complicated, even in insects.

So, when we look at, for example, the wasp that parasitizes orb weaving spiders, scientists have found that in the spiders that are zombified, what the wasp does, it lays an egg on the spider.

The egg hatches, and the wasp larva essentially piggybacks on the spider and drinks from it like it's a living juice box.

And the spider just goes about its business until the larva is ready to reproduce.

And then somehow the wasp larvae is manipulating the spider to think that it's time to molt so that the spider makes a different type of web than it normally does, something called a resting web.

It's reinforced and it's meant to support the spider and protect the spider while it's molting.

And then once that web is done, the wasp larvae drains the spider dry.

The spider's empty husk of a corpse drops to the ground, and the wasp larvae builds its cocoon and sets itself up in the spider's final web to hang out until it becomes an adult wasp.

So basically,

the spider is

convinced by this this wasp larvae in some way to build a cocoon for it.

It uses all of its final webery to like build a really nice little house for the wasp to grow up in.

I like final webery, yeah.

So, so what scientists found is that when spiders start making that final web, their little spider brains are being flooded with ectosteroids, which is the hormone that the spider naturally releases when it's ready to build a molting web.

So, it's actually, it's almost like it's taking a page out of the spider's existing biochemistry.

And scientists aren't sure yet if what the wasp larvae is doing is: like, is the larvae actually producing the ectosteroid?

Is it somehow triggering its production in the spider through another compound?

That's something that they're still figuring out.

But clearly, it's something that is already sort of baked into the spider's biology.

That

this is a chemical trigger that lets it know now it's time to build this kind of web.

Except this time, it's not going to survive the process.

So it is sort of a like

you couldn't necessarily get the spider to do something that it

wouldn't be able to do under any other circumstances, but you can like puppet it to do things that it might do otherwise.

That seems to be the much more common strategy among zombifiers, but exactly how they're being activated

is still a question.

Why is it important to understand sort of more about how this behavior manipulation works?

Yeah, that's a really good good question.

And it is one that we will answer after the break.

Support for Unexplainable comes from Anthropic, the team behind Claude.

Claude is an AI that can help you explore different angles on all kinds of questions.

Like the other day, I was watching the Red Sox and they played this sound after a strikeout.

And I was like, huh, I don't remember when that became a thing.

But it also wasn't something that I could just search for easily.

So I asked Claude.

He gave me some sources.

I tracked them down.

And before I knew it, I had the definitive history of the...

I also use Claude when I'm curious about genuinely complicated things.

I'll ask it something big.

We'll go back and forth to hone exactly what I'm looking for.

And yeah, it does get things wrong sometimes.

But when I double check or ask for a citation, it'll give me a better source.

Now, it's important to know how to use Claude well.

Like ask it follow-up questions.

Actually check out the citations it gives you.

But if you do, Claude can be a powerful tool.

It helps me find articles and primary documents that I never would have come across.

And it helps me dig wider and deeper, all while staying in control of the digging.

You can try Claude for free at claude.ai/slash unexplainable and see why the world's best problem solvers choose Claude as their thinking partner.

I need a job with a steady paycheck.

I need a job that offers health care on day one for me and my kids.

I want a job where I can get certified in technical roles, like robotics or software engineering.

In communities across the country, hourly Amazon employees earn an average of over $23 an hour with opportunities to grow their skills and their paycheck by enrolling in free skills training programs and apprenticeships.

Learn more at aboutamazon.com.

with the Spark Cash Plus Card from Capital One.

You can earn unlimited 2% cash back on every purchase and you get big purchasing power so your business can spend more and earn more.

Stephen Brandon and Bruno, the business owners of SandCloud, reinvested their 2% cash back to help build their retail presence.

Now, that's serious business.

What could the Spark Cash Plus Card from Capital One do for your business?

Capital One, what's in your wallet?

Find out more at capital1.com slash sparkcash plus.

Terms apply.

Scientists still have a lot of questions about the precise mechanics of zombification.

But if they could learn more about how zombifiers take over their victims, it turns out they could learn a lot that might benefit all of us.

This, in a lot of ways, is looking at really big questions about how behavior works, which is something that is

like scientists are still piecing this together on so many levels for all different types of organisms because there are so many factors that shape behavior.

Some of them are genetic, some of them are biochemical, some of them have to do with environment, some of them have to do with social relationships.

So this is one way of

trying

to understand behavior writ large.

You mentioned that these insects suppress the immune systems of their hosts.

Is there stuff that we could learn from that about

how immune systems work in general?

Oh yeah, looking at the immunosuppressive aspect of zombifiers is definitely something that is a huge area of interest because that could inform the development of immunosuppressive drugs, which is just something that would be hugely beneficial to people.

Right.

Not that this should be all about what's in it for me, but that is usually a consideration for scientific research.

Could there potentially be applications for this that have medical applications?

And so there is not yet a direct line between any research into how zombifiers evade their host's immune system and the development of some kind of pharmaceutical immunosuppressive.

But that's definitely something that is part of the mix when scientists are following that line of investigation.

I think about all the insects that invade homes,

some of which are beneficial, some of which are less so.

Could we potentially borrow from this to like fight off pests?

Pest control is definitely one avenue that scientists have explored as a way of, okay, well, you know, is there some way that we can take what we're seeing these zombifiers do to insects and apply it to insects that we don't like?

So baculoviruses, which are these viruses that infect caterpillars and make them climb and then dissolve their bodies into goo, this is something that has been deployed as a strategy for pest control in China and in Europe, in the US, in Brazil.

So these types of viruses, they're an interesting alternative to traditional insecticides because they are very targeted.

They are less toxic to the environment.

They're not harmful to insects that are not their host species, and they're not toxic to people.

But they're not as quick.

as I think the insecticides that people have gotten used to.

And people like things to be quick and they like them to be absolute.

So what seems like is the best way is perhaps to incorporate this alongside insecticides and use this along with other approaches because there are a lot of benefits to just, you know, going, going full-on zombie warfare to get rid of our agricultural pests.

Is there any attempt to like design our own to be like, all right, we really want to get rid of American cockroaches?

Like you are describing the plot of a zombie movie right now where a team of scientists are working with, they're studying zombie bugs and they're like, oh, hey, wouldn't it be great if we could manufacture an artificial version of this zombie virus and release it into the wild?

What could possibly go wrong?

Oh, no, the hubris.

Well, this does kind of get to a question that I have around all of this, which is maybe a silly question, but like,

could humans be zombified this way?

Are we also susceptible to this?

Well, there are

some types of pathogens that are known to manipulate behavior in mammals and indeed in humans too.

So rabies, of course, has been around and has been, there have been medical cases of rabies-infected humans that are thousands of years old with documentation of the heightened aggression.

So there is already a virus among us that can manipulate human behavior.

And recently, there have been studies into into toxoplasma gandhi,

which is the pathogen that causes toxoplasmosis.

So

this is an organism that its definitive host is cats.

So

it's very entrenched amongst human populations.

And in fact, many, many people, millions of people carry toxoplasma Gandhi, but it doesn't cause any symptoms.

It tends to be dangerous in people that are pregnant or in immunocompromised immunocompromised people.

Most of the people who are carrying taxoplasma Gandhi have no symptoms.

However, there have been studies recently in the last 10, 15 years or so, that have looked at people who are carrying the parasite and have found that there does seem to be evidence of certain types of behavior, of being

more risk-taking,

of being bolder.

In some groups, women being being more nurturing.

And what's interesting about it is that Toxoplasma Gandhi is known for manipulating behavior in rodents.

And what it does is it makes them bolder and less afraid of cats because Toxoplasma Gandhi needs to reproduce inside cats.

So it infects rodents and then to get back into a cat, it makes the rodent less afraid of and attracted to the smell of cat pea.

And that brings the rodent closer to a cat than it would normally go.

And then, once it's eaten, then the parasite is back inside the cat.

And scientists have found that this is true for other animals too.

So, hyena cubs that are infected with Toxoplasma Gandhi are bolder around lions and are more likely to be eaten by lions.

Chimpanzees that are infected with Toxoplasma Gandhi lose their fear of jaguars.

And some studies found that people who are infected with Toxoplasma Gandhi are more likely to make risky business decisions or be bolder in traffic.

So

there's still a lot of work to be done because obviously human behavior is its own form of complicated, but there is some evidence that seems to suggest that toxoplasma gandhi can shape human behavior too.

What?

Did I just blow your mind?

Yes.

That's so.

I can send you links to the studies.

I think I was expecting you to be like, no, unless you have rabies, you're definitely not.

Well, do you have a cat?

No, I don't.

I have to.

So

there could literally at this moment be zombifiers within us shaping us in some way.

It's entirely possible.

But there are so many things that make us.

who we are that shape how we behave there are environmental factors there are social factors.

The responsible answer.

Oh, sure, but you know, there might also be zombifiers.

In a world where a team of scientists they're working with, they're studying zombie bugs, and they're like, Oh, hey, wouldn't it be great if we could manufacture an artificial version of this zombie virus and release it into the wild?

What could possibly go wrong?

Everything goes wrong.

Kill them!

Kill the cockroaches.

You can't kill a cockroach if it's already undead.

Guys, I think Gregor might have just turned into a cockroach.

Coming soon under the kitchen sink near you.

There are so many more weird, wonderful zombie stories in Mindy Weisberger's book.

that is, Rise of the Zombie Bugs.

So if you want to read about zombified cicadas or fungi that will remind you of the show The Last of Us or any number of other skin-crawling, mildly horrifying things, please check it out.

This episode was produced by me, Bert Pinkerton.

It was edited by Sarah K.

Kramer.

Meredith Hodnott runs our show.

Noam Hasenfeld makes the music.

Christian Ayala did the spooky sound design and the mixing on this episode.

Melissa Hirsch did not enjoy all the gross bug stuff, but she powered through and checked the facts anyway.

Thanks, Melissa.

And the fact is that Julia Longoria and Jorge Just are just lovely human beings.

Thanks to Brian Resnick always for co-creating the show.

Thanks to Jonah for helping.

Thanks to Charlie Harding.

Claire White, Sergio Scardinho, and Angela Chen for their voice work.

And thanks to you for listening.

If you have thoughts about this episode, we are at unexplainable at vox.com.

I love hearing from you all, so please email us.

If you want to support the show and help us keep making it, please join our membership program.

It is at vox.com slash members, and you'll get ad-free podcasts, unlimited access to Vox journalism.

And if you tell our bosses that you signed up because you loved Unexplainable, it goes a long way.

So that is at vox.com slash members.

You can also support us by leaving a nice rating, perhaps, or a review, or just by telling people in your life to listen.

But Unexplainable is part of the Vox Media Podcast Network, and we will be back in your feed next week.

Adobe Acrobat Studio, so brand new.

Show me all the things PDFs can do.

Do your work with ease and speed.

PDF spaces is all you need.

Do hours of research in an instant.

With key insights from an AI assistant.

Pick a template with a click.

Now your prezzo looks super slick.

Close that deal, yeah, you won.

Do that, doing that, did that, done.

Now you can do that, do that, with Acrobat.

Now you can do that, do that with the all-new Acrobat.

It's time to do your best work with the all-new Adobe Acrobat Studio.

Time.

It's always vanishing.

The commute, the errands, the work functions, the meetings, selling your car?

Unless you sell your car with Carvana.

Get a real offer in minutes.

Get it picked up from your door.

Get paid on the spot.

So fast you'll wonder what the catch is.

There isn't one.

We just respect you and your time.

Oh, you're still here.

Move along now.

Enjoy your day.

Sell your car today.

Carvana.

Pickup fees may apply.