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How to Survive a Fast, Venomous, Flesh-Destroying Snake

The boy was thirteen years old when, while hunting for bush rats, he stuck his hand down the wrong hole. He was bitten by a saw-scaled viper. The boy’s hand swelled up and his skin turned white. He started bleeding from huge open gashes in his knuckles and arms. Worse still, the flesh in his hand started rotting.

The saw-scaled viper or carpet viper, Echis carinatus, Photograph by imageBROKER, Alamy
The saw-scaled viper or carpet viper, Echis carinatus, Photograph by imageBROKER, Alamy

Kempaiah Kemparaju from the University of Mysore in India shows me photos of the venom’s handiwork, and they’re hard to stomach. By the final image, the boy’s hand is a red, pulpy mess, and two fingers are missing. It looks like he reached into some kind of industrial machine.

The graphic images are, sadly, commonplace. Most snakes are harmless to humans, and even dangerously venomous ones are unlikely to bite us or to inject much venom. But the saw-scaled viper is a rare exception. It’s aggressive and hard to spot. It’s common to parts of the world that are densely populated by humans. And it has a potent venom. Toxins in the venom can break down the membranes that line our blood vessels, and max out our ability to clot, leading to catastrophic bleeding.

But the venom doesn’t just kill; it destroys.

It devastates the tissues around the site of the bite, so that even if people survive, they can still lose fingers, toes, or entire limbs. It’s estimated that around 125,000 people die from snakebites every year, but around 400,000 more face amputations. Antivenoms don’t help. They consist of large antibodies that are too big to effectively move from the blood into tissues that are being attacked. They save lives, but not limbs.

But we’re a little closer to a solution because Kemparaju and his colleagues, Gajanan Katkar and Kesturu Girish, have finally discovered how the viper’s venom wreaks so much havoc.

The team knew that the immune system reacts to viper venom by deploying white blood cells to the site of a bite. They suspected that some of these cells—the macrophages—might be inadvertently damage tissue, so they started isolating them. In the process, they snagged another kind of white blood cell, too—the neutrophils. What the hell, they thought. Might as well study the neutrophils too.

Good thing they did.

Neutrophils can sacrifice themselves to kill microbes by bursting open and releasing a tangled mesh of their own DNA. These webs, which are loaded with antimicrobial molecules, immobilise and kill invading cells. Rather aptly, they’re called neutrophil extracellular traps, or NETs.

When Kemparaju’s team saw the DNA threads under a microscope, they realised that neutrophils were also releasing NETs in the presence of viper toxins. But there, they do harm. The mesh blocks blood vessels and trap venom toxins at the site of the bite, where they attack local tissues. Those tissues also starve of oxygen, quickening their demise. Indeed, when the team injected viper venom into mice with low levels of neutrophils, the rodents succumbed to the venom but didn’t show any signs of tissue damage.

This leaves an unenviable choice. The actions of the neutrophils destroy tissue. But without them, the toxins circulate all over the body, damaging more organs and potentially killing the victim outright. The latter, incidentally, is what cobra venom does. It contains an enzyme called DNase that slices through the NETs and releases the trapped toxins.

Saw-scaled vipers lack DNase, which is probably a good thing on balance. “If the venom did have DNase activity, the systemic toxins along with the tissue-degrading enzymes would damage vital organs in no time, and a victim’s chances of survival would have been feeble,” says Kemparaju. It’s like this, he says: “Instead of life, you give your limb.”

But there might be a way to save both life and limb.

When the team injected mice with venom and DNase at the same time, the rodents died more quickly than they did with venom alone. But if the team waited for an hour or two before injecting the DNase, they prevented tissue damage without reducing the rodent’s odds of survival. “With our mice, we have achieved 100 percent success,” says Kemparaju. “Even if you administer the DNase three hours after the venom, you can prevent the loss of limb.”

“The results are very exciting, as they open up a potential new therapy for treating the debilitating, horrific, and destructive effects of certain snake venoms,” says Nicholas Casewell at the Liverpool School of Tropical Medicine. Still, the team must run clinical trials to ensure that DNAse treatments are safe and effective in people. Timing is everything, and the enzymes can do more harm than good if given at the wrong moment. And people would still need antivenoms to deal with the toxins already circulating in their blood.

“It will also be very interesting to see whether DNases will also reduce the local tissue effects caused by other snakes, such as puff adders and spitting cobras, thereby providing a generic treatment,” adds Casewell.

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A Fossil Snake With Four Legs

Snakes can famously disarticulate their jaws, and open their mouths to extreme widths. David Martill from the University of Portsmouth did his best impression of this trick while walking through the Bürgermeister Müller Museum in Solnhofen, Germany. He was pointing out the museum’s fossils to a group of students. “And then my jaw just dropped,” he recalls.

He saw a little specimen with a long sinuous body, packed with ribs and 15 centimetres from nose to tail. It looked like a snake. But it was stuck in unusual rock, with the distinctive characteristics of the Brazilian Crato Formation, a fossil site that dates to the early Cretaceous period. Snake fossils had been found in that period but never that location, and in South America but never that early. The combination of place and time was unusual.

Tetrapodophis specimen. Credit: Dave Martill.
Tetrapodophis specimen. Credit: Dave Martill.

“And then, if my jaw hadn’t already dropped enough, it dropped right to the floor,” says Martill. The little creature had a pair of hind legs. “I thought: bloody hell! And I looked closer and the little label said: Unknown fossil. Understatement!”

“I looked even closer—and my jaw was already on the floor by now—and I saw that it had tiny little front legs!” he says. Fossil-hunters have found several extinct snakes with stunted hind legs, and modern boas and pythons still have a pair of little spurs. “But no snake has ever been found with four legs. This is a once-in-a-lifetime discovery.”

Tetrapodophis forelimb. Credit: Dave Martill.
Tetrapodophis forelimb. Credit: Dave Martill.
Tetrapodophis hindlimb. Credit: Dave Martill.
Tetrapodophis hindlimb. Credit: Dave Martill.


Martill called the creature Tetrapodophis: four-legged snake. “This little animal is the Archaeopteryx of the squamate world,” he says. (Squamates are the snakes and lizards.) Archaeopteryx is the feathered fossil whose mish-mash of features hinted at the evolutionary transition from dinosaurs to birds. In the same way, Martill says, the new snake hints at how these legless, slithering serpents evolved from four-legged, striding lizards.

There are two competing and fiercely contested ideas about this transition. The first says that snakes evolved in the ocean, and only later recolonised the land. This hypothesis hinges on the close relationship between snakes and extinct marine reptiles called mosasaurs (yes, the big swimming one from Jurassic World). The second hypothesis says that snakes evolved from burrowing lizards, which stretched their bodies and lost their limbs to better wheedle their way through the ground. In this version, snakes and mosasaurs both independently evolved from a land-lubbing ancestor—probably something like a monitor lizard.

Tetrapodophis supports the latter idea. It has no adaptations for swimming, like a flattened tail, and plenty of adaptations for burrowing, like a short snout. It swam through earth, not water.

It hunted there, too. Its backward-pointing teeth suggest that it was an active predator. So does the joint in its jaws, which would have given it an extremely large gape and allowed it to swallow large prey. And tellingly, it still contains the remains of its last meal: there are little bones in its gut, probably belonging to some unfortunate frog or lizard. This animal was a bona fide meat eater, and suggests that the first snakes had a similar penchant for flesh.

Martill thinks that Tetrapodophis killed its prey by constriction, like many modern snakes do. “Why else have a really long body?” he says. In particular, why have a long body with an extreme number of vertebrae in your midsection? None of the other legless lizards have that, even burrowing ones. Martill thinks that this feature made early snakes incredibly flexible, allowing them to throw coils around their prey.

Their stumpy legs may even have helped. It’s unlikely that Tetrapodophis used these limbs to move about, and they don’t seem to have any adaptations for burrowing. With tiny “palms” and long “fingers”, they look a little like the prehensile feet of sloths or climbing birds. Martill thinks that the snake may have used these “strange, spoon-shaped feet” to restrain struggling prey—or maybe mates.

Tetrapodophis catching a lizard. Credit: James Brown, University of Portsmouth
Tetrapodophis catching a lizard. Credit: James Brown, University of Portsmouth

But is it even a snake? “I honestly do not think so,” says Michael Caldwell from the University of Alberta, who also studies ancient snakes. He says that Tetrapodophis lacks distinctive features in its spine and skull that would seal the case. “I think the specimen is important, but I do not know what it is,” he adds. “I might be wrong, but that will require me to see the specimen first hand. I’m looking forward to visiting Solnhofen.”

It’s certainly possible that Tetrapodophis could be something else. In the squamates alone, a snake-like body has independently evolved at least 26 times, producing a wide menagerie of legless lizards. These include the slow worm of Europe, and the bizarre worm-lizard Bipes, which has lost its hind legs but has kept the stubby front pair. True snakes represent just one of these many forays into leglessness.

Susan Evans from University College London, who studies reptile evolution, is on the fence. “This happens every time a possible early snake is described,” she says. “Opinions on snake evolution are highly polarised.”  She says that Tetrapodophis has some features you’d expect from an early snake, and doesn’t easily fit into any other known group of squamates. The specimen is also more complete than many other recently alleged snakes, some of which are known only from fragments of vertebrae or jaw. “Unfortunately, the skull is poorly preserved and this complicates interpretation,” says Evans. “The most important thing is that it is now brought to notice and it will be thoroughly scrutinised by other workers.” Above all, she hopes that someone finds one with a better skull.

Martill insists that Tetrapodophis has “got loads of little things that tell you it’s a snake.” There’s the backwards-pointing teeth, the single row of belly scales, the way the 150 or so vertebrae connect to each other, and the unusually short tail. (In lizards and crocodiles, the tail can be as long as the entire body, but a snake’s tail—everything after the hip—is relatively short.) Some of these features are found in other legless lizards, but only snakes have all of them. And Martill adds that you just wouldn’t expect an ancestral snake to have all the features that its descendants picked up over millions of years of evolution.

He also teamed up with Nick Longrich at the University of Bath to compare Tetrapodophis’s features to those of both modern and fossil snakes. Their analysis produced a family tree in which Tetrapodophis came after the earliest known snakes like Eophis, Parviraptor, and Diablophis, but is still very much a snake.

But how could that be? Eophis and the others only have two legs, so how could four-legged Tetrapodophis have come after them? The answer is that evolution doesn’t proceed along simple, straight lines. Even if four-legged lizards gave rise to four-legged snakes, then two-legged snakes, then legless ones, the later stages don’t displace the former ones. For a long time, they would all exist together, in the same way that birds co-existed with the feathered dinosaurs that gave rise to them. (This, incidentally, is also the answer to that tired question: “If we evolved from monkeys, why are there still monkeys?”)

“At any one time in the Cretaceous, chances are you’ve got ten, twenty, maybe thirty species [of early snakes], all going off on their own evolutionary paths,” says Martill. “There would be a whole bunch of very snake-like lizards, all with the potential to become today’s snakes. One of them does. Maybe one of them goes off and loses its front legs and retains its back legs for 20 million years. One maybe loses its back legs and keeps its front legs—and we haven’t found that one yet.”

Reference: Martill, Tischlinger & Longrich. 2015. A four-legged snake from the Early Cretaceous of Gondwana. Science http://dx.doi.org/10.1126/science.aaa9208

The Dawn of Snakes

Dinosaurs are Mesozoic superstars. The largest literally overshadowed other forms of life during their prehistoric heyday, and even now they attract far more attention than any other group of ancient organisms. It’s easy to forget the diverse and disparate species that wove together the ecology that helped support the dinosaurs we are so enchanted by.

This is especially true of the Late Jurassic Morrison Formation. These rocks yielded some of the first dinosaurian superstars – Diplodocus, Stegosaurus, Allosaurus, Ceratosaurus, and more – but in 1987 paleontologist George Callison wanted to remind his colleagues that there was an entire array of “wee fossils” that were often forgotten about. In a paper published by the Museum of Western Colorado in Fruita, Callison highlighted the mammals, smaller crocodiles, pterosaurs, lizards, and other diminutive players that inhabited the same floodplains among the likes of Apatosaurus. Among the lot were a few bones that seemed to mark the early days of a lineage still around us today – fossils that looked as if they belonged to an archaic snake.

The serpent wasn’t published when Callison wrote his paper. And other experts weren’t so sure the bones belonged to a snake. Utah state paleontologist Jim Kirkland, who helped fill in some of the background for this post, remembers that the fossils were too ambiguous to definitively assign to a snake. A lizard seemed a better fit, and this made sense given that snakes and lizards are close evolutionary cousins of each other in the reptile group called squamates.

Almost three decades later, though, Callison has been vindicated. The specimen he alluded to has just been confirmed as among the earliest known snakes. Together with three other species, the Jurassic reptile helps draw back the origin of snakes much further back in time.

From previous finds in Africa, North America, Europe, and South America, paleontologists knew that snakes had evolved by about 100 million years ago and could be found around the globe. They weren’t quite like serpents alive today – some still had hind limbs sticking out from their bodies – but they were undergoing a rapid radiation. From this diversity, paleontologists suspected that they weren’t looking at the origin of snakes so much as an evolutionary bloom already in progress. There were probably older, more archaic snakes. The trick was finding them.

A fossil block containing bones assigned to Parviraptor. From Caldwell et al., 2015.
A fossil block containing bones assigned to Parviraptor. From Caldwell et al., 2015.

The dawn snakes had been hiding in plain sight for years. A problematic block of 140 million year old fossils from England had helped conceal them. The Jurassic slab contains a variety of small reptile bones, most of which seemed to be from lizards. Some of these bones were given the name Parviraptor and were interpreted as those as a lizard, and they became the standard for interpreting similar fossils found elsewhere. Little bones from Colorado and Portugal, for example, were interpreted as lizards because of their similarity to the bones from England. But University of Alberta paleontologist Michael Caldwell and colleagues have now recognized these fossils as the earliest snakes.

Caldwell and coauthors have named four new snake species spanning 167-143 million years ago, drawing the origin of snakes back over 67 million years into the heart of the Jurassic. The oldest – Eophis underwoodi – is represented by parts of 167 million year old jaws, while Portugalophis lignites lived 155 million years ago in Portugal and the reinterpreted Parviraptor estesi inhabited England about 140 million years ago. And Callison’s fossils have finally been confirmed as falling in the ophidian ranks – the bones he alluded to have been named Diablophis gilmorei, a snake that slithered over fern-covered floodplains about 155 million years ago.

A restoration of Diablophis by Julius Csotonyi.
A restoration of Diablophis by Julius Csotonyi.

All of these snakes were small, but their exact size is uncertain. Too little is left of them to tell; just pieces of jaw and vertebrae from the front half of their bodies. But these seemingly sparse remains are still enough to tell that Diablophis and kin really are snakes. Even though snakes are modified lizards, they can be distinguished by features of their skulls and teeth. For example, snakes both ancient and modern have short, strongly-recurved teeth with shallow roots and three-sided tooth sockets.

Even though these ancient snakes probably looked different than those sliding along their bellies today – they likely still had hind legs, for starters – Caldwell and colleagues argue that the fossils show the typical snake skull evolved very early in the group’s history. A snake is not defined by a long, legless body, but rather by shared features that show up in the skull. (The same is true of other groups of animals – whales are not united by blowholes or blubber, but by a thickening of part of their ear bones.) This means that the very first snakes were probably almost indistinguishable from their lizard ancestors, identifiable primarily by subtle skull features.  As paleontologists continue to search for early serpents, Caldwell and coauthors write, “the fossil record of snake evolution will likely reveal four legged, short bodied ‘stem snakes’ that possess ‘snake’ skull anatomies.” The hunt for the four-legged snakes is on.


Caldwell, M., Nydam, R. Palci, A., Apesteguía, S. 2015. The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution. Nature Communications. doi: 10.1038/ncomms6996

Callison, G. 1987. Fruita; A place for wee fossils, in Averett, W.R., ed., Paleontology and Geology of the Dinosaur Triangle: Museum of Western Colorado, Grand Junction, Colorado. pp. 91–96.

Science Word of the Day: Kleptothermy

You could bask in the sun to remedy the cold. That’s a classic reptile way of working some warmth back beneath those scales. But there’s another option. You could steal your warmth. All you’d have to do is find some seabirds.

There’s a specific term for this warmth-sucking behavior – kleptothermy. The conditions, laid out by François Brischoux and colleagues, are really quite simple. There has to be a warm animal in a relatively cool environment and another animal that can use that body heat to raise their own body temperature. For example, a blue-banded sea krait that got nice and cozy in a wedge-tailed shearwater burrow.

When not in the underground nest, the researchers found, the sea krait had a body temperature of about 89ºF. Pretty warm for an ectotherm. But when the snake coiled up inside the seabird nest, out of the way of the owners, its body temperature was more stable and rose to about 99ºF. This was definitely because of the birds. When the accommodating avians weren’t at home, the lack of their body heat caused the nest temperature to dip to 82ºF.

The snake wasn’t the only reptile to borrow a little body heat. Other reptiles, from lizards to crocodiles, have been known to inhabit the burrows of warmer-bodied animals, as well as termite mounds where the activity of all the little insects keeps the colonies on the toasty side. And in a much broader study published this year, Ilse Corkery and colleagues found that tuataras are little kleptotherms, too.

Spare a little warmth? Henry the Tuatara. Photo by KeresH, CC BY 3.0
Spare a little warmth? Henry the Tuatara. Photo by KeresH, CC BY 3.0

Tuataras – which look like lizards but belong to a different group of reptiles called rhynchocephalians – face heating problems just like the sea snakes. In fact, scientists have found that the spiny reptiles are most comfortable with body temperatures between 67 and 73ºF. The trouble is that the temperature in the nighttime forest can dip below their preferred range, and basking back to a more tepid temperature the next day can take a while. So many tuataras seek out bird burrows to spend their nights.

After following the reptiles and taking temperature readings over three years, Corkery and coauthors found that many tuataras clambered into burrows made by fairy prions. Those that did so maintained higher body temperatures thanks to the bird-warmed air of the burrows. This probably let the reptiles start the day with a higher body temperature, reducing the time needed to bask in the sun the next morning and increasing the tuataras’ chances to spend much of the day foraging for insects and frogs.

Of course, mammals show similar behaviors. The difference is that mammals typically maintain high, constant body temperatures and share the warmth with each other. Although that knowledge is cold comfort when your significant other snuggles up to you with ice cold hands or feet. In such moments, you may be the victim of kleptothermy.


Brischoux, F., Bonnet, X., Shine, R. 2009. Kleptothermy: an additional category of thermoregulation, and a possible example in sea kraits (Laticauda laticaudata, Serpentes). Biology Letters. doi: 10.1098/rsbl.2009.0550

Corkery, I., Bell, B., Nelson, N. 2014. Investigating kleptothermy: A reptile-seabird association with thermal benefits. Physiological and Biochemical Zoology. 87 (2): doi: 10.1086/674566

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Pregnant Snake Prepares For Motherhood By Eating Toxic Toads

Some expectant mothers prepare for the arrival of their babies by reading books of parenting tips, painting nurseries, and buying a pram. The tiger keelback snake takes a different approach. When females get pregnant, they slither into the forest to eat as many poisonous toads as they can find.

The tiger keelback is a beautiful orange, olive, and black creature found in Japan. It defends itself with two glands on its neck, which contain poisons called bufadienolides. These irritate the airways and harm the hearts of any would-be predator. But the snake doesn’t make these poisons itself. Instead, it gets them from the toads it eats. It is immune to these poisons and shunts them into its own glands, defending itself with the pilfered defences of its own prey.

Deborah Hutchinson from Old Dominion University, Virginia discovered the tiger keelback’s thievery back in 2008. She showed that baby keelbacks that are raised in captivity are born without poisons, but quickly build up a supply if they can eat some toads. A wild-born snake doesn’t have this problem. Its mother laces her eggs and yolks with her own stolen poisons, arming her babies with chemical defences even before they hatch.

To do that, pregnant females need to find toads. After all, they’re eating poison for two.

Yosuke Kojima and Akira Mori from Kyoto University tracked the movements of 24 tiger keelbacks and found that females noticeably change their behaviour when they get pregnant.

These snakes live in a diverse area that includes forests, grasslands, riverbanks, and rice fields, all of which are teeming with amphibians. For the most part, the snakes stick to grasslands, where their favoured prey—two non-toxic species of frog—can be found in huge numbers. These frogs account for 89 percent of their food. By contrast, the Japanese common toad—the only local species that makes bufadienolides—is rarer, makes up just 1 percent of the snakes’ diet, and lives only in the forests.

Japanese common toad. Credit: Yasunori Koide
Japanese common toad. Credit: Yasunori Koide

But in early summer, while males are still sticking to grass, pregnant females spend a third of their time in the forests. There, they are unusually active and they hunt a lot of toads, which Kojima and Mori confirmed by checking their stomach contents.

The duo also placed several snakes in a Y-shaped maze. One arm was smeared with wet paper that had been rubbed on a toxic toad, and the other was daubed with the essence of a non-toxic frog. The male snakes always headed towards the path that smelled of poison-free prey. The females usually did the same but the pregnant ones flipped their preferences and went after Eau de Toad instead.

All of this strongly suggests that the pregnant snakes deliberately seek out poisonous prey. That’s not a trivial thing to do. The toads are much rarer than the snakes’ usual prey, so it costs more energy to find them. But the effort is presumably worth it.

When baby tiger keelbacks hatch in late summer, their jaws are too small to swallow toads. They have no way of building up their own bufadienolides until the next spring, when smaller, younger toads appear. By then, a predator could easily have killed them. But their mothers, by going the extra mile to stock up on toxins, provide them with defences to see them through this vulnerable window. These snakes practice a kind of toxic nepotism: the females that amass the greatest chemical wealth can give their children the greatest start in life.

Reference: Kojima & Mori. 2014. Active foraging for toxic prey during gestation in a snake with maternal provisioning of sequestered chemical defences. Proceedings of the Royal Society B. http://dx.doi.org/10.1098/rspb.2014.2137

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Cave-Exploring Snake Robot Gets Inspiration From Sidewinders

Three years ago, a robotic snake called Elizabeth slithered into Egyptian caves to search for long-hidden ships.

The caves lie on Egypt’s east coast, and contained the dismantled remnants of vessels that the Egyptians used to sail the Red Sea. They were discovered about a decade ago and some have surrendered their secrets with relative ease. Others, however, are too dangerous and unstable for people to explore.

Enter Elizabeth. The serpentine robot, built by Howie Choset at Carnegie Mellon University and named after his wife*, was designed to explore spaces that humans cannot. She can slide over rough terrain, slink through tight cracks, and manoeuvre around rubble. During her Egyptian field test, she performed beautifully, with one major exception: When the team tried to drive her up sandy slopes, she slipped and slid.

Real snakes face the same problem, and many desert-dwelling species have solved it through a bizarre technique called sidewinding. It’s a very counter-intuitive style of movement. From above, it looks like the snake is travelling sideways in a beautiful undulating wave. But it leaves behind a series of straight tracks, each the length of its body.

The trick to understanding the technique is to realise that the snake is never sliding. Instead, it is constantly picking itself off from its current position and laying itself down in a new spot. The head goes first, and the rest of the body follows. But before the body catches up completely, the head is off again. At any point of time, the snake is only touching the ground with two short parts of its body. That’s why it moves in a wave, but leaves a straight track.

Sidewinding is perfect for negotiating dunes. Rather than pushing against slippery sand, the snake’s rolling motion means that it’s mostly in static contact with its surface. Many species of snake can do this, but only two have truly mastered the technique—a rattlesnake from the US and Mexico, and a horned viper from Angola and Namibia. Confusingly, both are called sidewinders.

Choset’s robot Elizabeth could sidewind, but not very well. It was missing something that its real counterparts were doing.

Elizabeth, the robot snake. Credit: Nico Zevalios and Chaohui Gong.
Elizabeth, the robot snake. Credit: Nico Zevalios and Chaohui Gong.

To discover that mystery ingredient, Choset teamed up with Daniel Goldman from the Georgia Institute of Technology. For decades, Goldman has been fascinated by how animals move on and through sand. He has studied baby sea turtles as they clamber over a beach, and a pointy-nosed lizard called the sandfish as it swims through sand. And his team have built robots that emulate these animals, to reveal the physics behind their movements. Guy knows sand; guy knows robots. And as luck would have it, he was already starting to study sidewinders.

The team, led by postdoc Hamidreza Marvi and student Chaohui Gong, worked with six sidewinders (the American kind) from Zoo Atlanta. They put the snakes on a sandy trackway that could be inclined at different angles. They even trucked in sand from Arizona’s Yuma Desert to give the snakes material that they would normally face in the wild. “They’re excellent study subjects,” says Goldman. “They sidewind on command. Put them in a container and off they go.”

At first, the team assumed that as the track got steeper, the sidewinders would respond by digging their bodies more firmly into the ground, just like we would if we climbed a steep dune. They didn’t. Instead, they kept more of their body in contact with the ground, giving themselves more purchase on increasingly treacherous slopes. As the researchers raised the flat track to a 20 degree incline, the sidewinders compensated by laying down twice as much body.

The team also tested 13 other species of rattlesnake from Zoo Atlanta. None of them sidewind naturally, and none of them could negotiate the same slopes that the sidewinders could. They tried to climb straight up, and failed. “It was quite amusing,” says Goldman. “One of the comments we got from our reviewers was that it was obvious what the sidewinders do. Well, it wasn’t obvious to the other snakes!”

The team then programmed Elizabeth to mimic the sidewinders, and found that she suddenly became much better at moving up slopes. Her performance revealed that snakes have to stick within a certain range of contact lengths, and this range narrows as the slopes get steeper. If they don’t lay down enough body, they slip. If they lay down too much, they can’t lift the rest of themselves effectively, and run into the sand in front of them. They end up digging a hole, rather than making progress.

So, by playing with their robot, the team understood more about what the snakes do. And by studying the snakes, they improved their robot. “Using our understanding of fundamental engineering, we advanced these robots very far but we couldn’t get them up sandy hills,” says Choset. They only surmounted that final hurdle by studying nature.

Choset thinks that the snake-bots have many possible uses. They could search for survivors trapped in collapsed buildings. They could also inspect dangerous environments like nuclear storage facilities. And, of course, they could explore archaeological sites. “If we have the opportunity to return to Egypt, we’d use this capability,” he says. “Archaeology is like search and rescue except everyone’s been dead for thousands of years so there’s no rush.”

* Choset tells me that there was a second snake robot called Howard, but he was lost in some airline baggage mix-up. Samuel L. Jackson was unavailable for comment.

Reference: Marvi, Gong, Gravish, Astley, Travers, Hatton, Mendelson, Choset, Hu & Goldman. 2014. Sidewinding with minimal slip: Snake and robot ascent of sandy slopes. Science http://dx.doi.org/10.1126/science.1255718

More on animal robots:

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To Protect An Endangered Snake, First Protect A Venomous One

If you go for a walk through the rocky hills of Finland’s Aland archipelago, you might come across a medium-size snake with gunmetal grey scales and darker diamonds running down its back. It looks a little bit like an adder, but it can’t be because its head is thin and tapered…

Wait, did that snake just change its head?

You can’t be sure, but now its head is definitely flat and triangular—the defining shape of adders and other vipers. That means it’s venomous. There are people living nearby, with kids and pets. You decide to kill the snake with a rock. That was a poor decision, especially since the dead snake wasn’t an adder. It was a smooth snake—completely harmless, rather endangered, and now very slightly more endangered.

The smooth snake is found throughout Europe but its populations are small and thinly scattered. It could be easily wiped out, so the European Union has listed it as a specially protected species. In Finland, it’s classified as “vulnerable”, and may be bumped up by one degree of concern to “endangered”.

For much of its existence, the smooth snake protected itself by mimicking the far more dangerous adder, and its charade (especially its shape-shifting head) is good enough to fool even trained biologists. But this disguise is now the snake’s undoing. The fear of venomous snakes might compel birds to flee, but it sometimes compels humans to kill the potential threat.

This is doubly problematic for the smooth snake because its brand of mimicry (known as Batesian mimicry) only works if the noxious creature it mimics is plentiful. If an island contains a lot of adders, birds soon learn that attacking a long thing with a triangular head and a diamond back is a very bad idea. That’s good for the smooth snake, whose predators avoid it too. But if an island contains no adders, birds could attack the smooth snakes with impunity. Why wouldn’t they? They’re never come to associate those markings with possible death. Batesian mimics should always be in the minority if their copycat acts are to work.

Johanna Mappes from the University of Jyvaskyla in Finland showed this in 1997, by creating an artificial example of mimicry. She injected mealworm larvae with a foul-tasting liquid, and stuck small sugarballs (the ones used to decorate cakes) onto their heads—these were the models. She stuck the same balls onto other mealworms without the nasty liquid—these were the mimics. She then presented both groups to great tits in varying ratios. Mappes found that if the number of mimics equalled or exceeded that of the models, the benefits of their disguises disappeared.

This is bad news for the smooth snake. On Aland archipelago, they already outnumber adders. If Mappes is right, their defence should already be worthless. “For the successful conservation of smooth snakes in Aland, it seems crucial to also protect adders,” writes Mappes, along with colleague Janne Valkonen. “Our results provide foresight to prevent a potential disaster in a situation where a mimic becomes endangered due to the decreased frequency of its model species.”

This might apply to other species too. Many harmless snakes mimic venomous ones, and many snake populations are crashing all over the world. The smooth snake example suggests that protecting an endangered mimic is when an endangered species mimics a dangerous one, we might need to protect both to save the former—a one-for-the-price-of-two deal.

Reference: Valkonen & Mappes 2014. Resembling a Viper: Implications of Mimicry for Conservation of the Endangered Smooth Snake. Conservation Biology http://dx.doi.org/10.1111/cobi.12368

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Homing Pythons Re-Enact Homeward Bound

In the Disney film Homeward Bound, two dogs and a cat undertake a perilous journey through the American wilderness to try and find their way home.

This story is the same but instead of pets, we have six giant snakes.

The Burmese python can grow up to 5.7 metres in length, making it one of the world’s largest snakes. As its name suggests, it hails from south-east Asia, but the exotic pet trade unleashed it upon the USA. Since 2000, these giants have spread across 1,000 square kilometres of Florida’s wetlands, suffocating local mammals and birds (and the odd alligator) along the way.

In 2006, Shannon Pittman from the University of Missouri-Columbia travelled to the Everglades National Park and implanted a dozen pythons with radio transmitters to track their movements. As part of that study, she put six of the snakes in sealed plastic containers, and drove them to locations 21 to 36 kilometres away before releasing them.

Pittman expected the snakes to randomly wander about their new environment. That is not what happened.

Instead, the pythons slithered home.

All of the them started moving towards the places where Pittman had originally captured them. Their accuracy was incredible. They stayed within 22 degrees of the right homeward bearing, and within 3 to 10 months, five of them had ended up within five kilometres of their original position.

This map shows their movements. Each colour represents a different snake. They were captured at the circles, taken to the triangles, and ended up at the diamonds. They all did spectacularly well. Even the blue snake seems to have headed in mostly the right direction before veering off for whatever reason.

Credit: Pittman et al, 2014.
Credit: Pittman et al, 2014.

Homing pythons!


Many animals, from pigeons to salmon to spiny lobsters, have incredible navigational skills, but this is the first time that any snake has demonstrated a similar acumen. They must have some sort of compass sense because they kept the right bearing, and they must have an internal map because they knew when they had reached the right destination.

For a compass, they could be picking up on the position of the sun or stars, the smell of home, or changes in the Earth’s magnetic field. As for the map, the snakes were always transported in sealed containers so they couldn’t memorise cues about their journeys as some animals do. They must be using some cues in their environment to work out their position but, again, we have no idea what those cues might be. (I would personally love it if they turned out to have a magnetic sense because I’ve written about such senses extensively—but really, who knows?)

Pittman suspects that this navigational prowess may have contributed to the Burmese python’s skill as an invader, allowing them to explore new terrain in confidence and expand their range more quickly. The discovery may also help scientists to better predict and control the snakes’ movements.

Reference: Pittman, Hart, Cherkiss, Snow, Fujisaki, Smith, Mazzott & Dorcas. 2014. Homing of invasive Burmese pythons in South Florida: evidence for a map and compass senses in snakes. Proc Roy Soc B http://dx.doi.org/10.1098/rsbl.2014.0040

Related: Invasive Pythons Can Find Home 20 Miles Away, Study Says

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The Sad Tale of the Thirsty, Dehydrated Sea Snake

It is the bitterest of ironies that a snake which spends its entire life at sea, constantly submerged in water, should spend months on end being thirsty and dehydrated.

Fresh water quenches thirst. Salt water worsens it. If you drink seawater, your kidneys try to get rid of the excess salt by diluting it in urine, and you expel more water than you take in. The same applies to other land animals, and those that return to the sea have special adaptations for coping with salt. Many sea animals avoid swallowing seawater entirely, and get fresh water from the food they eat. Turtles, sea birds and marine iguanas have special glands for getting rid of salt.

Sea snakes have similar glands under their tongues. When Harvey Lillywhite from the University of Florida started studying these serpents a few decades ago, all the textbooks said that they used these glands to get rid of salt.

But that explanation didn’t add up. For a start, Lillywhite found it very hard to keep one of these gland-bearing species in full seawater—they would often become very dehydrated. Later, he discovered that three species of sea kraits refuse to drink seawater even when they become dehydrated. In the lab, they always choose fresh water. In the wild, they tend to stick close to sources of fresh water, like springs or rainy spots. It looked like their ability to process salt was a myth.

Sea kraits are well adapted for life in the ocean, but they return to land to lay their eggs. The yellow-bellied sea snake, however, is completely marine. This beautiful creature, with its black and yellow body and paddle tail, hunts at sea and gives birth to live young at sea. It’s the only species of sea snake to live in the open ocean. Surely, these snakes would have some way of coping with salt?

Lillywhite started studying this species in 2009, at a site off the coast of Costa Rica. “We’ve looked at hundreds,” he says. “No sea snake we’ve observed has drunk any seawater.”

They only stick to the fresh stuff, but the amount they drink varies throughout the year. These snakes live in a place that goes through drought from November to May. If they were captured during these dry spells, they betrayed their thirst by sipping heavily from fresh water; if they were caught in wetter months, they barely drank. “If the snake drinks fresh water, it’s thirsty,” says Lillywhite. “If it’s thirsty, it’s dehydrated, and if it’s dehydrated, it’s not doing what the textbooks said.”

The team also found that the snakes had significantly less water in their bodies than in the dry months than in the wet ones. Despite having a salt gland and being surrounded in water, the snakes are thirsty and dehydrated for months on end. Lillywhite thinks that they cope by having an unusually high amount of water in their bodies to begin with. They might also have adaptations that help them to lose water slowly, and to withstand the effects of dehydration.

In the wild, it is possible that the snakes use deep springs or estuaries, but they are incredibly widespread and Lillywhite has never found any evidence of them congregating in specific sites.

Instead, rain brings them salvation. When it falls over the ocean, it doesn’t mix with the seawater straight away. Instead, it forms a layer that is either fresh or only mildly salty. If the conditions are right, these “freshwater lenses” can be both deep and persistent. And the yellow-bellied sea snake, it seems, drinks from them.

Lillywhite thinks that it should be easy for them to find such lenses because they regularly surface to breathe. They might also be able to sense the changes in pressure that accompany a storm, and head for areas where rain is likely to fall. “When you scuba dive you can sort of tell when it’s raining,” he says. “I think the snakes can too.”

And if rain never falls, the snakes may not survive. Many sea snakes that were once abundant off the coast of Northern Australia have mysteriously started to vanish. Eight species are locally extinct. There are many possible causes, but Lillywhite notes that this part of Australia has recently suffered from a prolonged drought. Perhaps the lack of falling fresh water contributed to their downfall? Perhaps, surrounded by water, these sea snakes died of thirst.

Reference: Lillywhite, Sheehy, Brischoux & Grech. 2014. Pelagic sea snakes dehydrate at sea. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2014.0119

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Rattlesnakes Two Hours Apart Pack Totally Different Venoms

If you’re walking through the flat desert of Phelan, California, and you’re bitten by a Southern Pacific rattlesnake, you will start to bleed badly.  The snake’s venom is loaded with proteins that break down the walls of your blood vessels and that prevent the now-leaking blood from clotting.

Let’s say you survive. You bid goodbye to the desert and drive up some twisting mountain roads to the town of Idyllwild, swapping Joshua trees for pine trees. But the Southern Pacific rattlesnake lives here too, and you get bitten again. And this time, the venom doesn’t go for your blood. The toxins of these snakes include proteins that stop nerves from sending signals into muscles. They start to paralyse you.

It takes two hours to drive between these two sites. In one, you’ll find a rattler with purely haemotoxic (blood-destroying) venom. In the other, you’ll find snakes of the same subspecies with purely neurotoxic (nerve-destroying) venom.

Scientists who study snake venom know that it’s an incredibly variable weapon. Its composition can differ dramatically between different species, subspecies, individuals, or even sexes.

Still, the differences between the Phelan and Idyllwild snakes are extreme. “It’s the most complex variation that I’ve ever seen especially within such a geographically short distance,” says Bryan Fry from the University of Queensland, who led the study that team that analysed the different venoms. Even the haemotoxic venoms varied considerably in how potent they are, what toxins they contain, and what targets those toxins attack.

Fry suspects that the rattlesnakes use such diverse cocktails because they live in such different environments. The Idyllwild snakes, in particular, live on high mountain ridges that are 1,600 metres above sea level. They are extremely isolated from the other populations. “It’s like they’re on islands,” says Fry.

The mountains also contain different prey to the deserts, and the snakes there might need to kill their prey more quickly. “Your ability to track prey is very different if you’re in a rocky outcrop than if you’re in grassland. If an animal gets away, it might disappear down to a crack and you’ll never see it again,” says Fry. “We hypothesise that the neurotoxic venoms are needed to drop the prey faster.”

If that’s the case, why don’t all the rattlesnakes have the faster-acting venom? It may be that the desert-dwellers simply haven’t had the pressure to stray from their traditional haemotoxic blends, or that their venoms are adapted to killing their local prey. The short answer is: we don’t know. We barely know what these different populations eat, let alone how their venoms are adapted to killing those prey.

“It’s a perfect example of the importance of basic evolutionary studies,” says Juan Calvete, a venom researcher from the Biomedical Institute of Valencia. In 2012, he found a similar pattern in the Mojave rattlesnake from southern Arizona, whose venom also changes from haemotoxic to neurotoxic as you from east across the state. “Geographic variability in venom composition [within a species] seems to be the rule rather than the exception, particularly for wide-ranging species,” says Calvete. “However, the variability is unpredictable, and must thus be experimentally determined.”

Indeed, people who are bitten by rattlesnakes often experience very different symptoms and complications depending on where they are. For example, Calvete’s team found that if you’re bitten by a Mojave rattlesnake in Cochise County rather than in neighbouring Pima County, you’re 10 times more likely to die.

In California alone, around 800 people are bitten by rattlesnakes every year. Although just a handful die, the venom is painful, debilitating, and can lead to lengthy hospital stays. To make things worse, Fry says that the antivenom that Americans use for rattlesnake bites—CroFab—is ineffective against the Southern Pacific rattler.“It’s notoriously poor,” he says. “People have to be kept in the hospital for up to a week getting continuous infusions just to keep them alive.”

There are two problems. First, CroFab uses antibodies that are less allergenic than those in other antivenoms, but get cleared from the body very quickly. “You end up with very expensive urine,” says Fry. Second, it doesn’t contain antibodies that target the specific proteins used by the Southern Pacific rattlesnake. “They were relying on toxins to be similar to stuff from other rattlesnakes, but even within this one [subspecies], you get completely different venoms. It’s been a debacle.”

Fry thinks that both the effectiveness of antivenoms and our ability to care for patients will be greatly improved if we get a better understanding of the idiosyncracies of venom in local snakes.

The media should take note too. Several news reports have suggested that rattlesnakes in southwest USA are becoming deadlier, and rapidly evolving more toxic venom. Fry says that’s rubbish—the venoms are naturally very varied, and evolved that way a long time ago. It’s not the toxins that have recently changed, but our appreciation of just how diverse they are.

Reference: Sunagar, Undheim, Scheib, Gren, Cochran, Person, Koludarov, Kelln, Hayes, King, Antunes & Fry. 2014. Intraspecific venom variation in the medically significant Southern Pacific Rattlesnake (Crotalus oreganus helleri): Biodiscovery, clinical and evolutionary implications. Journal of Proteomics.

More on venom evolution:

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80-Year-Old Vintage Snake Venom Can Still Kill

On the morning of 28 July, 1950, Kevin Budden walked up to a roadside in Queensland, Australia with several feet of angry snake coiled around his arm, and flagged down a truck.

Budden, aged 20, was already an experienced snake handler, who specialised in collecting venomous species. The era of venom research in Australia was just taking off, and men like Budden were instrumental in capturing the serpents that scientists used to make antivenoms.

The taipan was high on his list. Its brown body grows up to 3 metres long and its yellow head can deliver one of the most potent venoms of any snake. At the time, there was no antivenom.

As wonderfully recounted by David Williams, Budden and his friends had already failed to catch a taipan the previous year. This time, it took him four weeks of searching before he finally found one, hidden under some rubbish and about to eat a rat. He managed to subdue the snake with his foot and grabbed its neck. The taipan was enraged and Budden, unable to get it into a sack, simply walked to the nearest road, still holding it by the neck. A friendly (and probably alarmed) truck driver took him to a local snake-catcher, who confirmed that Budden had—finally—caught a taipan.

But by now, Budden’s hand was cramped and sweaty. His grip faltered when he finally tried to lower the taipan into a bag, and it bit him on the hand. He was taken to hospital, but died the next day. There was, after all, no antivenom.

Even after he was bitten, Budden seemed more concerned for the snake’s safety than his own. He insisted that the taipan shouldn’t be harmed, for it was still tremendously useful for research. Everyone honoured his wishes. The taipan was taken to Melbourne and milked for its venom before itself dying a few weeks later.

Fifty-eight years later, Bryan Fry was rummaging through some dusty boxes at the University of Melbourne’s famous Australian Venom Research Unit (AVRU) when he came across a treasure trove—vial upon vial of vintage venom.

The stocks were part of the collection of Straun Sutherland—a legend among aficionados of venomous creatures, and the founder of the AVRU. He passed away in 2002 and Fry, the then deputy director of the AVRU, was going through the uncatalogued parts of his inventory.

He was amazed by what he found. These weren’t just any old samples. They had been collected by the so-called “snake men”: an amazing group of herpetologists, including Budden, who trekked through the outback and collected the most dangerous snakes around. From the 1930s and onwards, they captured tiger snakes, brown snakes, taipans, and more, so they could be milked for their venom. These samples were used to make antivenoms that have saved countless lives. And Fry was looking at them. There, for example, was the venom of the taipan that killed Kevin Budden.

“It was like opening a time capsule,” he says. “It gave me goosebumps. These were very personal samples to us. To be working with the milkings from that exact snake… these weren’t just letters on the side of the tube. They had historical and emotional value.”

They also had something that Fry did not expect—toxicity. Even though some of them were 80 years old, they could still kill.

It’s not like the samples had been carefully prepared. They had been crudely dried, kept in glass tubes with rubber stoppers, and stored at room temperature rather than in a freezer.

Still, Fry’s team found that they contained the same cocktail of proteins and had the same toxic effects as venom that had been recently collected from modern snakes of the same species. Death adder venom from the 1960s could still stop neurons from communicating with muscles. Taipan and tiger snake venom from the 1950s could still clot blood. The only vial that contained ineffective venom was also the only one where the rubber seal had eroded. Otherwise, the toxins were in great shape.

To Fry, the collection isn’t just a vault of historical artefacts. It’s also a goldmine for research. “Now we’ve shown that they’re stable, we’re going to be continually working with them,” he says.

Why? Because there’s a long history of developing important medicines from animal venoms, and Fry is always on the lookout for substances that could lead to tomorrow’s drugs. And the greater the diversity of venom he has to work with, the more likely he is to find something.

Some of the samples in the historical collection were taken from populations of snakes that have since been wiped out. At least 12 percent of snakes are currently threatened with extinction, and Fry believes we should intensify our efforts to collect venom samples now, while we still have the chance. It’s clear that once collected, those samples can be used for experiments for decades, even if their donors disappear.

Other samples came from snakes that no one has milked since, like tiger snakes living on four Australian islands. Since island animals are genetically isolated from their mainland counterparts, and face different evolutionary pressures, they often evolve in new and unusual ways. “The venoms from the islands are most likely to contain something interesting,” says Fry. “[These samples] save us the trouble of going to there ourselves.”

Reference: Jesupret, Baumann, Jackson, Ali, Yang, Greisman, Kern, Steuten, Jouiaei, Casewell, Undheim, Koludarov, Debono, Low, Rossi, Pangides, Winters, Ignjatovic, Summerhayers, Jones, Nouwens, Dunstan, Hodgson, Winkel, Monagle & Fry. 2013. VINTAGE VENOMS: PROTEOMIC AND PHARMACOLOGICAL STABILITY OF SNAKE VENOMS STORED FOR UP TO EIGHT DECADES. Journal of Proteomics. Citation tbc.


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Painkilling chemicals with no side effects found in black mamba venom

The black mamba has a fearful reputation, and it’s easy to see why. It can move at around 12.5 miles (20 kilometres) per hour, making it one of the world’s fastest snakes, if not the fastest. Its body can reach 4.5 metres in length, and it can lift a third of that off the ground. That would give you an almost eye-level view of the disturbingly black mouth from which it gets its name. And inside that mouth, two short fangs deliver one of the most potent and fast-acting venoms of any land snake.

Combined with its reputation for aggression (at least when cornered) and you’ve got a big, intimidating, deadly, ornery serpent that can probably outrun you. It’s not the most obvious place to go looking for painkillers.

But among the cocktail of chemicals in the black mamba’s venom, Sylvie Diochot and Anne Baron from the CNRS have found a new class of molecules that can relieve pain as effectively as morphine, and without any toxic side effects. They’ve named them mambalgins.


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Since pythons invaded, Florida’s mammal populations have crashed

It turns out that if you unleash giant snakes into a place that didn’t previously have giant snakes, the other local animals don’t fare so well. That seems obvious, but you might be surprised at just how badly those other animals fare.

Since 2000, Burmese pythons have been staging an increasingly successful invasion of Florida. No one knows exactly how they got there. They normally live in south-east Asia and were probably carried over by exotic wildlife traders. Once in America, they could have escaped from pet stores or shipping warehouses. Alternatively, overambitious pet owners could have released when they got too large for comfort. Either way, they seem to be thriving.

With an average length of 12 feet (4 metres), the pythons are formidable predators. They suffocate their prey with powerful coils, and they target a wide variety of mammals and birds. The endangered Key Largo woodrat and wood stork are on their menu. So are American alligators (remember this oft-emailed photo?). Conservationists are trying to halt the spread of the giant snakes, out of concern that their booming numbers could spell trouble for local wildlife.

Michael Dorcas from Davidson College thinks they are right to be concerned. In the first systematic assessment of the pythons’ impact, Dorcas has found that many of Florida’s mammals have plummeted in numbers in places where the snakes now live.


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Snakes know when to stop squeezing because they sense the heartbeats of their prey

To fans of cheesy pop music, the beat of someone else’s heart is a symbol of romantic connection. To a boa constrictor, those beats are simply a sign that it hasn’t finished killing yet.

A constricting snake like a boa or a python kills its prey by suffocation. It uses the momentum of its strike to throw coils around its victim’s body. Then, it squeezes. Every time the prey exhales, the snake squeezes a little more tightly. Soon, the victim can breathe no more.

We’ve known this for centuries but amazingly, no one has worked out how the snakes can tell when to stop constricting. Scott Boback from Dickinson College has the answer. Through its thick coils, a boa can sense the tiny heartbeats of its prey. When the heart stops, the snake starts to relax.


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Meet the Agta, a tribe where a quarter of men have been attacked by giant snakes

When Thomas Headland first met the world’s longest snake, he was on the way to the toilet. He was living in the Philippine rainforest with a group of hunter-gatherers called the Agta. On the walk to the outhouse behind his hut, he stumbled across a reticulated python curled up on the trail. “The hairs on the back of my neck stood up and I shouted for help,” he recalls. At his cries, six to seven Agta jumped up from the surrounding bushes… and started laughing. Their new American neighbour had fallen for the old previously-killed-python-on-the-path gag. “I didn’t know what jokers these people were at the time,” says Headland.

Giant snakes frequently attack people in fantasy and science-fiction stories, but such attacks are not merely the stuff of fiction. Through his extensive work with the Agta, Headland has found that a quarter of all the men have been attacked by pythons.