the toad and the pufferfish

One day in 1980, a man claiming to be called Clairvius Narcisse showed up in a rural Haitian village. This came as something of a surprise to the villagers, since Narcisse had supposedly died in 1962, and was subsequently buried. The new arrival claiming to be Narcisse said he'd been turned into a zombie after his "death," forced with other zombie slaves to work on a sugar plantation at the behest of his "master," a voodoo priest. He claimed his own brother had put the plan in motion, since the two had quarreled over land ownership. The brother had since died, so the sudden reappearance of Narcisse to claim the inheritance raised a few suspicions, to say the least. Yet the newcomer knew certain facts of the dead man's life that only Narcisse himself, it seemed, could have known. He claimed he'd been drugged into submission, and when the master died, and the drugs wore off, he regained his memory and sanity.

Narcisse was a rare case, but not the first such occurrence of purported zombification. In 1937, novelist and scholar Zora Neale Hurston was researching Haitian folklore when she came across the case of Felicia Felix Mentor, who died and was buried in 1907 at the age of 29, and was rumored to have been zombified. Hurston heard rumors that zombies in Haiti were created using strong drugs, but couldn't verify them. Still, she predicted, "If science ever gets to the bottom of voodoo in Haiti and Africa, it will be found that some important medical secrets, still unknown to medical science, give it its power, rather than gestures of ceremony."

Enter Canadian ethnobotanist Wade Davis, who made a pretty strong case for the pharmacological basis of zombification in his 1985 book, The Serpent and the Rainbow, which I devoured (figuratively) in high school in a single night. It was that fascinating. (Also, as a child, zombies scared the hell out of me, along with werewolves. Somehow, reading a science-y book placing it within the context of reality dissipated any lingering anxiety on that score. Davis also penned a more scholarly tome, Passage of Darkness: The Ethnobiology of the Haitian Zombie, in 1988.)  He investigated the strange case of Narcisse, and in the process somehow gained unprecedented access to the secret voodoo rituals involved in creating zombies. (This also raised some ethical questions, since he apparently observed the desecration of graves.) But Davis did discover that voodoo priests relied on complex powders in their rituals. The ingredients differed according to region, but of seven of the eight samples he managed to collect contained pufferfish, a marine toad, a hyla tree frog, and human remains. The first two are the most pertinent, since both animals secrete powerful neurotoxins.

Neurotoxins are chemicals that change the way the neurons in the brain function, either by inhibiting the release of certain neurotransmitters or enhancing them to harmful levels. There's around 100 billion neurons in the brain, controlling muscle contractions (motor neurons) by carrying electrochemical signals from the central nervous system to the muscles, or conveying sensory signals from the outer parts of the body to the central nervous system (sensory neurons). Interfere with this complex communication system, and you can interrupt speech, thought processes, motor function, even respiration. That's why neurotoxins provide such a useful hunting mechanism for creatures like the blue-ringed octopus, Australian paralysis tick, Japanese pufferfish and numerous snake and spider species.

The blue-ringed octopus' approach to feeding is especially gruesome: its venom is maculotoxin, which paralyzes but doesn't kill the prey, so said prey is fully conscious (inasmuch as one would consider the creature to have consciousness) as it is being eaten. We hope the octopus is, at the very least, quick, rather than choosing to slowly savor its meal. The good news, for the prey at least, is that the paralysis spreads rather quickly to the respiratory system and causes it to fail. Usually, human victims don't survive unless they receive oxygen immediately.

Maculotoxin is the venomous form of tetrodoxin, the neurotoxin of choice for the pufferfish (a.k.a., fugu), a gourmet delicacy because daredevil diners really like the tingling sensation the remaining traces of poison produce on the lips and tongue. Despite a stringent certification requirement for chefs to prepare fugu, a few people die each year from consuming it. Because accidents happen.

And here's where the zombies come in, because tetrodoxin is a key ingredient in Haitian zombification rituals. The other key ingredient is toxins produced by the sea toad (bufo Marinas) as a defense mechanism. Davis' book details the process by which the zombie poison is created. The toad is placed in a jar with a stinging sea worm and the ensuing conflict causes the toad to produce a lot of toxin, which is mixed with a bit of tetrodoxin from the pufferfish. A voodoo priest (boko) will poison a victim, causing him or her to become catatonic, and often mistaken for dead. Said victim is buried, the drug wears off after a few days, and the boko can exhume the "zombie." Ah, but how to get the victim to do the boko's bidding? Apparently, this is achieved via regular doses of datura stramonium (more commonly known as jimson weed), an extract of the thorn apple, which makes the victim docile and biddable.

Davis' theories are a bit controversial, however. True, when he applied his collected samples of the powders to the shaved skin of rats and a rhesus monkey, they became lethargic and immobile, but eventually recovered completely, and critics question whether these experiments were sufficiently controlled. (A few even believe Davis' research was fraudulent.) While the ritualistic practices he documents were further confirmed by British researchers in the 1990s, they didn't find any examples of real zombies. Usually, people labeled as such were suffering from mental diseases, such as catatonic schizophrenia or an organic brain disorder. In other cases, it was as simple as mistaken identity. In 2005, there were some sensational tabloid headlines about University of Pittsburgh scientists creating "zombie dogs," but in truth, the work was in cryogenics and suspended animation: the scientists successfully revived dogs who had been in suspended animation after three hours had passed, and two-thirds of the subjects suffered no brain damage. Still, they weren't "zombies." (And no, suspended animation and resuscitation for humans isn't even close to becoming a reality just yet. Suspending the animus can be done; it's the resuscitation part that's tricky.)

But there does seem be a living example of zombification in Nature. Via Zooilogix, we learned last week that scientists at Ben-Gurion University of the Negev in Israel have figured out how a certain species of wasp (the emerald cockroach wasp/jewel wasp, or Ampulex compressa) managed to turn poor, innocent cockroaches into their willing "zombie slaves." Lots of venomous creatures stun their victims before devouring them, but this particular species of wasp will sting its roach-y prey, so that the prey is able to walk, but can't do so of its own accord.

The predator-wasp literally has to grab the roach's antenna and lead it back to the wasp nest, much like leading a dog on a leash. There, instead of eating the roach, the wasp lays an egg on its belly, Eventually a larva hatches and devours the still-docile roach. It's not exactly laboring in the fields, but it is a handy solution to the problem of providing an ultra-convenient food to one's offspring. Nor is the roach-corpse wasted about the eating: the larva weaves its cocoon inside the corpse, eventually bursting out as a full-grown Ampulex compressa, eager to go out into the world and create its own zombie-roach horde. 

Okay, but what's going on, exactly, to achieve such a subtle control of the victim's behavior? BGU researcher Frederic Liberstat and his colleagues knew the secret lay in "a rich cocktail of toxins" that the wasp injects into its victims. And they also knew that the wasp makes two injections: once to subdue them, and then again delivering a more precise sting directly into the roach-prey's brain -- specifically, a section called the protocerebrum, which controls the escape reflex. The stinger has sensors along its side to guide it to the appropriate brain section.

The Ben Gurion scientists theorized that the venom blocks a key chemical messenger in the brain called octopamine. This chemical is what makes insects alert, motivates the to move and perform physical tasks. It serves a similar purpose as noradrenaline, a chemical messenger involved in the "flight or fight" response.

To test that hypothesis, they managed to replicate the effect by injecting cockroaches in the lab, and even figured out how to "un-zombify" the bugs by following up with an antidote injection. Many a New Yorker plagued by roach infestation might be tempted to buy a roach trap that makes use of the wasp's venom -- except then they'd just have a bunch of lazy zombie roaches lying about the apartment, having to led around by the antenna all the time. We'd need to figure out how to get one to behave like a bellwether, leading his catatonic cronies out into the street much like the Pied Piper led all the rats (and, later, the children) out of Hamelin.

Ironically, the same day I read about the zombie roaches, reminding me of the unfortunate Narcisse and the first time I read The Serpent and the Rainbow, I also noticed a post on BLDGBLOG entitled  "The Husband Who Would Not Die." A man named John Darwin went out canoeing some five years ago, and never returned, although eventually authorities recovered the wrecked canoe and a paddle. Five years later, John Darwin returned -- as a zombie! Um, okay, not really. Nor was it amnesia, kidnapping or anything else that makes for a good potboiler. Turns out he just didn't want to pay his bills, so he faked his own death and spent the next five years living in a secret passageway that connected his old master bedroom to another room next door. He and his wife had purchased adjoining properties 15 months before his disappearance. The entrance was through a closet, hidden by a wardrobe. Perhaps Darwin was a Narnia fan. At any rate, being dead wasn't all it cracked up to be, so he turned himself into the authorities. They've since sold those properties, no doubt to pay those long-overdue bills. We are so jealous of the new owner. There's nothing cooler than having your own secret passageway.

The upshot is, apart from the victims of the jewel wasp, though, it seems our fascination with zombies owes more to legend and superstition than actual science. (As a Monday morning diversion, take this fun little zombie quiz at Discovery Channel Website; you should score pretty well, provided you've absorbed the science in this post, and have seen the major zombie movies.) But just in case, the How Stuff Works page on zombies offers a few helpful hints on surviving a zombie attack along with classic mistakes to avoid -- like entering a zombie-infested building, leaving potential weapons about for zombies to wield, or locking yourself in a cellar without adequate supplies. I know I felt better after hearing I could probably outrun a zombie... provided I wasn't surrounded.

Comments

[Lab Lemming]

"Neurotoxins are chemicals that change the way the neurons in the brain function"

Don't most neurotoxins act on the central nervous system, and not the brain?

And the upshot of the blue ringed octopus that everyone who takes a basic first aid class in Australia knows is this: As long as you give rescue breathing, you can keep somebody with an octopus bite alive without permanent damage occurring, unlike snakes, snails, spiders, jellyfish etc., which tend to mess people up if antivenom is not available.

[Tom]

Cool! But your zooilogix link is borked. (missing the "zooillogix/" in the middle)
http://scienceblogs.com/zooillogix/2007/12/scientists_uncover_the_secret.php

[lpcprof]

Wonderful, entertaining blog, well-written. I will certainly check out The Physics of the Buffyverse.

[The Flying Trilobite]

I wonder if the wasp venom would work on other types of insects? I assume it is probably specific to local roaches near the wasps.

I'd rather have a bunch of zombie praying mantises doing my bidding than roaches. Think of the glowing zombie eyes of a mantis. Or control a whole choir of cicadas, keening, "Happy Birthday".