Real-life zombies

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0:42If this was you then, you might need MIDI now. Perimenopause can start 10 years before menopause.

0:48Mindy Weisberger:If you're experiencing symptoms like night sweats, weight gain, or anxiety, speak to the menopause experts at MIDI Health. Book a virtual appointment at joinmidi.com. Midlife needs MIDI. Results may vary. Medications prescribed only if clinically appropriate based on a consultation with a clinician. 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.

1:28But 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.

1:46Mindy Weisberger: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.

2:36And 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.

3:25So at a certain point, it stops walking.

3:27Mindy Weisberger: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 starts to pump out, this chemical signal alluring too, like a sexy fungal love perfume.

4:27That 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.

4:38Mindy Weisberger:All of this draws in new victims who, if everything works out, will soon be turned into their own fungal fly puppets.

4:52Mindy Weisberger: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 zombifier. 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 Bird Pinkerton. And today on the show, Mindy will tell us what we know and what we don't know about zombie bugs.

5:51Mindy Weisberger: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 sense, that's the cold virus generating a change in behavior.

6:41But 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.

6:54Mindy Weisberger: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. 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. Bugs, but the colloquial version of bugs. Exactly. I do have to apologize to entomologists because as far as entomologists are concerned, bugs are only insects with sucking mouthparts. However, as we all know, colloquially, bugs covers a much broader range.

7:46Mindy Weisberger:Poor entomologists. Do you have personal favorite zombifiers 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 hairworm. Now, the worm grows inside this cricket. It grows to the point where it is many times the length of the cricket itself, 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.

8:29So, you know, it's kind of like the movie Alien, right? Like you can see a foot, you can see an elbow. It's like, you know, 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 know, you really want to squick yourself out.

9:12Oh my God, it's like, oh! It's sick. There are many, many videos of this on YouTube. That is so freaking nasty.

9:20Mindy Weisberger:This is so gross. Tyler's getting a shame. 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 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 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 immune system, no, there's nothing to see here.

10:33You can just go about your business. You don't need to worry about me. So that's a big question. 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 house 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.

11:09Mindy Weisberger: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, the 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.

11:56The 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 larva builds its cocoon and sets itself up in the spider's final web to hang out until it becomes an adult wasp.

12:53Mindy Weisberger:So basically, the spider is convinced by this wasp larvae in some way to build a cocoon for it. It uses all of its final webbery to build a really nice little house for the wasp to grow up in. I like final webbery. Yeah. 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 larva is doing is, like, is the larvae actually producing the ectosteroid?

13:40Is 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.

13:59Mindy Weisberger: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 question. And it is one that we will answer after the break.

14:44Mindy Weisberger:Hey, it's Ryan Reynolds here for Mint Mobile. Now, I was looking for fun ways to tell you that Mint's offer of unlimited premium wireless for$15 a month is back. So I thought it would be fun if we made$15 bills. But it turns out that's very illegal. So there goes my big idea for the commercial. Give it a try at mintmobile.com slash switch. Upfront payment of$45 for three months,$90 for six months, or$180 for 12-month plan required. $15 per month equivalent. Taxes and fees extra. Initial plan term only. Greater than 50 gigabytes may slow when network is busy. See terms. Excuses are easy. An epic movie night?

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16:26Hey, oh, hey, hey, hey, zombie, zombie.

16:33Mindy Weisberger: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.

17:18So this is one way of trying to understand behavior writ large.

17:26Mindy Weisberger:You mentioned that these insects suppress the immune systems of their hosts. Is there stuff that we could learn from that about, like, how immune systems work in general? all. 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?

18:06And 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.

18:25Mindy Weisberger: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 U.S., in Brazil.

19:14So these types of viruses, they're an interesting alternative to traditional insecticides because they are very targeted. They're 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 full-on zombie warfare to get rid of our agricultural pests.

19:55Mindy Weisberger:Is there any attempt to design our own to be like, all right, we really want to get rid of American cockroaches? 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?

20:41Well, 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 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 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.

21:40It tends to be dangerous in people that are pregnant or in immunocompromised people. Most of the people who are carrying Toxoplasma 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 more nurturing. and what's interesting about it is that is that Toxoplasma gondii is known for manipulating behavior in rodents and what it does is it makes them bolder and less afraid of cats because Toxoplasma gondii 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 pee and that brings the rodent closer to a cat than it would normally go.

22:47And 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 gondii are bolder around lions and are more likely to be eaten by lions. Chimpanzees that are infected with Toxoplasma gondii lose their fear of jaguars. And some studies found that people who are infected with Toxoplasma gondii 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.

23:31What? Did I just blow your mind?

23:34Mindy Weisberger: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 two. 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?