Real-Life 'Zombie' Animals Walk The Earth Thanks To Thousands Of Parasites

Consider the ladybug. Our polka-dotted little friend spends its days munching aphids, climbing leaves, occasionally alighting upon a delighted child's outstretched finger, and generally beetling around being adorable. It's one of nature's most inoffensive critters, which is perhaps why the Dinocampus coccinellae wasp is such a troubling one by comparison.

See, in order to lay her egg, the mama Dinocampus must attack a ladybug with her stinger, and deposit an egg — and a virus — into her precious little abdomen. As the baby wasp grows, it sustains itself by eating the ladybug's insides, until the virus — which has infected the host's entire body — hits the brain and shuts down the central nervous system. This conveniently paralyses the ladybug while the larva erupts from her abdomen and spins itself into a cocoon.

That isn't the end of the ordeal, either; the virus then forces the ladybug to stand guard over her tormentor, periodically convulsing to fend off potential predators as the baby wasp grows into adulthood. For all intents and purposes, the ladybug is in a somnambulant fugue state, controlled by a mysterious virus it inadvertently acquired through violent means.

Because nature is terrible, this process replicates wherever ladybugs and Dinocampus cross paths. Because nature is a marvel, 25 per cent of the affected ladybugs actually survive it. The poor ladybug is far from the only creature to be subjected to this kind of torturous mind control, either; far from it. Zombies are real, and they walk — and crawl, and squirm — amongst us every day.

Such is the premise of science journalist Matt Simon's spine-tingling new book, Plight of the Undead: What Real Life Zombies Reveal About Our World — and Ourselves. In short, there are literally thousands of different kinds of viruses and fungi (as well as more evolved members of the animal kingdom) that have the power to exert control over the minds and bodies of other creatures via violent biological processes, done with the explicit goal of propagating their own species — on other words, to zombifying them.

Simon catalogues a number of these tiny puppet-masters, travelling to far-flung locales in search of zombie ants, killer shrimp (which are a particularly unpleasant sort), diabolical caterpillars, cunning birds, murderous bumblebees, and the beautiful jewel-toned wasps that perform complex brain surgery on unsuspecting cockroaches.

In keeping with the theme, he gamely compares these body-snatching beasts and their victims to the appropriate horror movie counterparts, from the shambolic Night of the Living Dead classic model to 28 Days Later's "fast zombies." Our guide also takes a more internal journey into the depths of his own existential dread.

Faced with living (and undead) examples of unimaginable suffering, Simon questions the cruelty of nature, explores the way that mind-controlling viruses have ravaged human society, informs us that one in three humans is strolling around with a zombifying parasite right now, and nearly disproves the existence of free will along the way. It's a fun read that will haunt you to your very core.

Toxoplasma gondii tissue cyst in a mouse brain. A correlation between the parasite and Intermittent Explosive Disorder (IED) in humans has been observed. IED causes people to react with inappropriate aggression. (Image: USDA, Read more here)

Perhaps even more unsettling than the smorgasbord of insanely vicious, stomach-turning deaths that pepper this book like so many spores is Simon's more nihilistic foray into the idea that free will isn't real. It's not a thing. We are mobile flesh towers programmed by millennia of DNA tweaks, powered by firing neurons and influenced by environmental stimuli. The ghost in the machine is just a series of smaller machines. Only the dead — and the undead — are truly free.

Despite the presence of complex, evolved thought processes in our big ol' human brains, Simon argues that, ultimately, we will do what we are biologically compelled to do. That is, unless our regularly scheduled programming is disrupted by something, say, a virus that makes us foam at the mouth and recoil from water... or one that edges us closer to schizophrenia, or suicide. If a viral invader like rabies or Toxoplasmosis makes an appearance, then we deviate from our neurobiological predestinations. We become... something else.

The takeaway here, of course, that nature is fucking terrifying, we're all just meatsacks stumbling around a dread planet full of undead horrors, and, if an alien fungus happened to hack into our brains and command us to betray our entire families, well, it could always be worse. Just ask the ladybug.

Gizmodo: Which of the creatures discussed in your book bears the closest resemblance to what we think of when we see the word "zombie" — the flesh-eating virus, the mind control, the desire to feed, the violent trajectory from victim to victim?

Matt Simon: That'd have to be the rabies virus. Which, OK, is kind of cheating, because it turns out that rabies was the inspiration for the zombie of pop culture that we know and love today. The roots of the zombie go way back to 17th century Haiti, but it wasn't until the early 20th century that the creature became truly rabies-like — the aggression, the extreme contagion, the general bitey-ness.

We all know rabies so well that it's easy to forget that it's in fact a parasite that manipulates the behaviour of its host to its own ends. It induces that aggression so the host ideally gets another victim in its teeth, thus transmitting the parasite.

But the manipulation even goes beyond that. The parasite makes its victims, including humans, not just shun water, but fear it. That's because it wants to keep its host's mouth full of virus-packed saliva. That in my opinion is way more diabolical than anything Hollywood could ever dream up.

Gizmodo: "Killer shrimp" was not a phrase I ever imagined I'd encounter, until I read your book. What were a few of the biological surprises you came across during your research?

Simon: Probably the biggest biological surprise from researching this book was just how incredibly widespread zombification is in nature. Viruses do it, same with bacteria, and worms and wasps and fungi and on and on. Which means it's both very real, and also a supremely useful strategy for an organism to evolve.

Not only that, but it's evolved independently within lineages. So the ant-zombifying fungus you've probably seen crawling around the internet is actually several species that independently evolved the technique. It didn't just happen once before each of the species split off from a common ancestor, but over and over in individual species.

A zombie ant infected with the Ophiocordyceps unilateralis fungus. (Photo: Katja Schulz, Flickr)

Related to that, another intriguing bit I still can't stop thinking about is that this is what we know about. Who knows what kinds of crazy manipulations are going on that science is ignorant to. Yes, it's amazing and by this point well-studied that a fungus can get inside an ant and order it around the rainforest with extreme precision, but what else is out there that might be even more mind-blowing?

Gizmodo: One of the creepier things that stood out to me was reading about the way that zombifiers like trematodes can shift the course of entire ecosystems. Can you explain this concept down a little bit here?

Simon: It's easy to forget we used to be lunch for a lot of critters, until we excused ourselves from the food chain and invented agriculture and factory farming. But ecosystems are wildly complex things, so it's easy to imagine how the zombifiers might make their mark. Scientists are just beginning to understand the scope of this.

One particularly interesting case are the trematodes you mentioned, which get into cockles and seize up their "foot" muscle, the bit that allows them to move up and down in the mud. So the cockles get stuck at the surface, where they're easier pickings for birds, which as it happens is the only place where the trematodes can complete their life cycle.

Thus the parasites are manipulating the ecosystem. On top of that, the cockles crowded at the surface form little spaces between their shells that serve as shelter for smaller critters. And that's just the workings of a single parasite. It's entirely likely that all ecosystems feel the impacts of at least one manipulative parasite.

Gizmodo: What does Plato's Allegory of the Cave have to do with eyeless fish?

Simon: The Allegory is all about perception, right — prisoners stuck in a cave only see shadows projected on a wall, so what they think is reality is a distortion. To really understand the zombies and their zombifiers, we have to realise that in a way, everything we see and hear and smell are distortions. Because while the universe is one objective reality, every organism experiences it subjectively.

This is the idea of the umwelt — your senses build your own biased outlook on the world, senses that have evolved for your particular need as a species.

The problem when it comes to manipulative parasites is this bias seeps into our understanding of these manipulations. We're liable to study only what we personally can see, since for most of us that's our primary sense.

So we can look at a raccoon freaking the hell out because it's got rabies in its brain, but what other kinds of manipulations are we totally ignorant to? How many parasites out there are changing the smell of their hosts, or the sounds they make? To truly understand the world of the zombifiers, we somehow have to climb out of our cave.

Gizmodo: How much do humans have to fear from these zombifiers?

Simon: A lot, as it happens. Rabies is the obvious one, so staying away from surly mammals is a good general rule. But more subtle parasites could be manipulating our behaviour. One particularly fascinating one is Toxoplasma. It didn't evolve to parasitise us, but instead rats. It gets in their heads and makes them straight up attracted to cat urine, which of course ends badly for the host. But not the parasite — it completes its life cycle in the bellies of felines.

But because we share the same generally mammalian brain as a rat, Toxo can get in our heads too. Scientists estimate that perhaps a third of humanity is infected, which is fine unless you're pregnant and it causes complications. But studies have shown some weird things going on with Toxo-infected people — it's been linked to suicide and risk-taking and even schizophrenia.

I mean, no need to run to the doctor to get tested, but it is a haunting reminder that we humans aren't special. We've got mushy brains that follow the same rules of the physical universe as every other animal, which means we're liable to get manipulated too.

Gizmodo: You disprove the existence of "free will" here. Did you set out to write such an existentially heavy book, or did it eventually just take on a mind of... er... its own?

Simon: Funny things start happening in your head when you spend a year writing about how seemingly easy it is for parasites to mind-control their hosts with either hormones or physically attacking the brain. By the way, I don't like believing there's no such thing as free will. For one, it's got a whole lot of implications for the very way our species operates, so there's that.

And a lot of people would disagree with an incorrigible materialist like me. But our brains are made up of neurons and neurotransmitters, just like other critters. We're not special — we just think we are.

Here's a good exercise. Think of a food. Now try to explain why of all foods you thought of that one. You didn't decide to think of that food — it just happened. Which makes sense in the grand scheme of things. Agonising over every "decision" to put on one sock before the other or wear a red sweater instead of a blue one is not an efficient way for a brain to operate.

Like, do you really need to "decide" to brush the top left quadrant of your teeth instead of the lower right? We're on autopilot, and in my opinion that includes higher level, less routine stuff. Sure, brushing your teeth is rather less consequential than "choosing" a college, but can you really claim to have chosen Stanford over UCLA? To think that thought, you would have had to think about thinking the thought, and think about thinking the thought about thinking the thought, and so on. Not super efficient.

The parsimonious explanation would be that we're drones at the mercy of our neurons, especially considering that imaging studies have shown that our brains are actually making decisions a few seconds before we even realise we're making those decisions.

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