Zombie caterpillars? Really? Is there such a thing?
Let’s look at the history of zombies and how such behaviors can arise in nature
The term zombie originates at least as far back as the 8th century in Africa, with its origins being found in the term nzambi, which in the Congo meant ‘spirit of a dead person,’ and ndzumbi meaning ‘corpse’ in the Mitsogo language of Gabon. From there, the term gravitated to Creole with African slaves, being used to describe someone who died and was then brought to life without speech or free will.
Europeans first became obsessed with zombies in Haiti, where the mortality rate among slaves was three times higher than in the US, and eventually led to revolution. The appalling treatment of slaves often left them in a zombie-like state before they succumbed to death, further perpetuating European fears. It’s a sad historical irony, that the monstrous actions of slave owners would breed what was essentially the racist blame of Africans becoming the undead. People fear things they don’t understand, and so witchdoctors were blamed for what was the inevitable result of slavery itself, and the walking dead were born, only instead of feeding on the living, they were clinging to the last vestiges of their own lives.
In 1968 George Romero transformed zombies from mindless slaves into aggressive predators, hunting the living. His film Night of the Living Dead launched the modern zombie genre, continuing today in shows such as The Walking Dead.
How realistic is a zombie apocalypse?
Well, that depends on a couple of factors. First, how likely is it a disease could bring about zombie behavior, and how well could it spread in the modern world.
Medical science describes the virulence of pathogens with the Basic Reproduction Number or R-0 (sometimes called R-Nought), and this can give us a good idea of how a zombie virus could spread and how we could combat it.
If R<1 then an outbreak is considered under control and fading, as for every person infected, less than one other person will contract the disease, meaning the wildfire is running out of fuel.
Ebola, as an example, had an R-0 factor of between 1.5 and 2, so without intervention, for every person infected, up to two other people would succumb to the disease. That might not sound particularly bad, but remember the law of compounding effects, doubling as it goes.
The Spanish Flu, which killed an astonishing 18 million people in the 1920s had an R-0 factor of just 2.8.
Measles, though, makes Ebola look like an amateur with an R-0 factor between 12 and 18. So for every infected person in an area without inoculation, almost twenty other people will become infected. Without intervention, the next generation of infections will reach 400, and the next, 8000. You can see why medical science worked so hard to develop a vaccine for measles, and why inoculation is so important.
Perhaps the most virulent virus to hit humanity is Smallpox, which, like Measles had an R-0 factor in the high teens, and may have even breached 1:20, being airborne as it spread.
In his book, Demon in the Freezer, Richard Preston recounts one of the last outbreaks where a patient was quarantined on the ground floor of a hospital, in an isolated ward. One of the nurses made the mistake of cracking the window to allow a breeze into the patient’s room. From there, the virus drifted up, through a second floor window, infecting patients in that room, and even people that never even entered that room. Merely walking down the corridor, past closed doors, was enough to expose victims to the disease!
Most people think we defeated Smallpox with vaccines. We didn’t. There wasn’t enough time to produce enough vaccine. Smallpox would take hold of cities containing millions of people. Even with a hundred thousand doses, the prospect of stopping this deadly disease seemed impossible.
The UN came up with the concept of ring containment. Rather than vaccinating everyone within a city containing tens of millions of people, they calculated how far the virus could spread once infection was reported, and they’d contain that area, vaccinating all of those inside the perimeter likely to come in direct contact with the virus, essentially forming a ring around the infection site. It was a stunning idea, and allowed humanity to drive the virus to extinction regardless of its virility. Today, there are no wild pockets of Smallpox, only demons in the freezer, held in stock by the US and Russia. Should these ever be unleashed as biological weapons, they would be utterly devastating.
What would be the R-0 factor of a zombie virus? Unlike Smallpox and Measles that have incubation periods, allowing them to spread unseen, the zombie virus is immediately apparent. Even if it matched the R-0 factor of Measles, I’m confident we could contain it. We’ve already battled worse in Smallpox.
All of this was in my mind when I wrote my young adult thriller What We Left Behind. I knew we could defeat a zombie virus, so how could I present a plausible alternative? How could something so devastating slip below our medical radar and spread until it was too late to contain?
I settled on the concept that the very idea of a zombie virus would be a distraction, diverting valuable resources on a wild goose chase, and instead proposed an inter-species parasite, a minor mutation to something that was already common, and so easily overlooked.
Last week, a friend sent me an article about researches at the University of California observing tomato plants releasing toxins that cause caterpillars to turn on each other and become cannibals.
Zombie caterpillars! Who would have thought of it? Science again beats science fiction hands down
And this isn’t the only example of zombies in nature. The flatworm, Euhaplorchis californiensis alters the behavior of the fish it infects, making it easier to be captured and eaten by birds? Why? It reproduces within the bird gut, and uses the fish to complete its lifecycle.
Then there’s the Ophiocordyceps fungus which turns ants into zombies.
Toxoplasma gondii reproduces in the gut of cats. The only problem is… the gut is a point of transit. So how can this microbe get back into a cat’s gut in order to reproduce? It can’t. Not by itself. So it faced an evolutionary dead-end, unless it adapted to manipulate another species, and quite remarkably, that’s exactly what happened.
Mice and birds become carries of T. gondii when they eat cat feces. Over time, natural selection developed a strain that would cause mice to become attracted to the smell of cat urine, effectively sacrificing themselves for their parasitic companion.
Scientists suspect the neurotoxin released by T. gondii may have a detrimental impact on humans as well.
Could zombies arise as the unintended side-effect of some other parasitic life-cycle like toxoplasmosis? Image credit: CDC
In What We Left Behind, I leave the culprit unnamed, but the book focuses on how to break the cycle of cross-species infection. It’s a great read.
If you’re into zombie bowling, or surfing with zombies, grab a copy. I think you’ll enjoy it.