Sunday, December 2, 2012

The 250 lb. Hamburger

“…so when a snake eats its prey, it’s like if you were to eat a 250 lb. hamburger, all in one bite, without using your arms!”

It’s 1997, I’m an English major at UC Berkeley, and I’m sitting in a classroom in the palatial Valley Life Sciences Building. This is a building that English majors do not frequent. The shiny white pillars hurt our bookish eyes. Yet I keep coming back, week after week, to a classroom filled with big cat skulls, stuffed egrets, and pickled frogs. By some fluke I have enrolled in a class called Natural History of the Vertebrates, which has nothing to do with my major. It is here that I first witness the hamburger magic trick.

Fifteen years later, the magic trick is still fresh in my mind. And magic it is. Not the rabbit-in-the-top-hat, saw-your-assistant-in-half kind of magic, but real-life magic. Teaching magic.

Making an analogy that allows students to see something from their point of view.
Magic, like most things in life, works best when greasy food is involved.

In that classroom at UC Berkeley, and in countless classrooms before and since, Dr. Harry Greene used the hamburger trick to help students understand one of the most mind-boggling processes in nature: how a snake with a mouth the diameter of a walnut can ingest a rabbit the size of a football… all with no hands.

A Western Diamond-backed Rattlesnake eats a large rabbit. 
J. Schofer

The hamburger trick, friends, is the subject of this post.

So how in the heck does a snake pull off this feat? Let’s start with the meat of it all—or rather, the bones and ligaments.

First things first: it is important to come to terms with the fact that our human skulls are boring.

In contrast, a snake’s skull is a thing of beauty and complexity—by all accounts, an exemplary marriage of structure and function, a marvel of evolution.
The skull of a Gaboon viper boasts impressive two inch-long fangs.

This post is an appetizer version of how-the-snake-skull-works. Keep in mind that I am greatly simplifying the following descriptions—another magicky thing us teachers try to do.

Here's how it works. Your jawbone (or mandible) is functionally a single bone. It articulates with your cranium in joints on either side, in front of your ears, that allow limited rotational movement of the jaw, allowing you to bite, chew, talk, etc.
"The last thing I remember, I was looking at a human skull in anatomy class. I must have died of boredom."

The setup is far more interesting in snakes. The jaw does not attach directly to the rest of the skull, but rather suspends from the skull via the quadrate bone. (You kinda have a quadrate bone, too, but it has migrated, over millions of generations, into your ear—a "hear bone.") 
The large quadrate bone in a reptile skull is shown at left. 

So, think of it as snakes having their jaws suspended from the rest of the skull via a mobile quadrate bone. The snake's quadrate bones can basically whirl around on each side. This funky attachment makes the snake’s mouth far more flexible than yours, and also makes the opening larger.

An egg-eating snake routinely eats eggs several time the diameter of its own head. Notice how the skin stretches between the scale rows. Read this blog for more on egg-eating snakes.
B. Bouton

Still not a big enough hole for Peter Rabbit, though. The trick is in the joint at the front of the jaw bone. Your jaw actually consists of two bones (dentary bones) that fuse together at this joint when you’re a fetus. In a snake chin, the dentary bones are connected with a stretchy ligament that allows the two sides of the jaw to stretch away from each other, allowing the mouth to open even larger.

This image from Digimorph shows nicely how the two dentary bones of the lower jaw are not connected with bone.
You can see the two sides of the jaw stretched far apart in this image of a python gorging on a sheep.

The articulation of the quadrate bone plus the elastic ligament at the chin allow the python's mouth to open large enough to eat huge prey— like deer, crocs... even humans

There’s much more to it than that—other moveable skull bones, super-stretchy skin, even a snorkel to help breathe while the maw is stuffed (yes, really!)—but I am hungry for a hamburger. 

(Note that snakes' jaws do not "unhinge" or "dislocate." Those are entrenched myths that arose from people trying to compare their jaws with our jaws. Let's keep it real, people.)
The upshot of the structural adaptations I have described above is that snakes can stretch open their mouths really wide—wide enough to ingest prey many times the diameter of their own head. Now we are ready for the main course:

“…so when a snake eats its prey, it’s like if you were to eat a 250 lb. hamburger, all in one bite, without using your arms!”

Sadie helps show us what a Macrostomatan Harry would look like sucking down a beast-sized burger. 
J. Furman

That’s a big burger. (A mere fraction of the world record burger, weighing in at a ton, but a big burger nonetheless.)

The record largest burger was made at a Minnesota casino in 2012. It had to be flipped with a crane. But I digress...

Now you can put it all together and watch Harry doing his magic here:

Abracadabra! That is how the magic is done.

Getting hungry? Eat like a snake.

Note: Harry Greene's book Tracks and Shadows: Natural History as Art came out in 2013. If you're still hungry, pick up this book (or his 1997 classic Snakes: The Evolution of Mystery in Nature) to read about some more amazing things snakes do!

Tuesday, November 27, 2012

Man-Eating Snakes

Snake architecture is superfically quite simple. Snakes are basically a long tube of muscle and gut, with a toothy mouth on one end and a pooper on the other.

This image can get pretty creepy when the snake is longer than a grown man and as big around as Mike Tyson's thighs. It turns out that the prospect of being eaten by something can drive a pretty strong evolutionary phobia. Some scientists even say that the reason our binocular vision is so acute is because of growing up with—evolutionarily speaking—big snakes that could eat you.

John Voight’s binocular vision couldn't save him from being eaten—then regurgitated and re-eaten—by a mammoth snakein the 1997 movie Anaconda.

Of course, anacondas don’t actually get that big. But they get plenty big. The anaconda—a denizen of swamps and rivers of Central and South America—is the world’s most massive snake, meaning it’s the heaviest but not the longest.


What can I say? Men in groups like to carry huge anacondas around.

Scientists debate the particulars, but the anaconda that takes the record was about 28 feet long, with a 44-inch circumference. What weight does that translate to? Probably about 500 pounds. Sheesh, that’d gobble up some serious human.

Of course, the majority of anacondas—even the biggest—content themselves on a diet of fish and wetland mammals, because these snacks are much more abundant than humans, and maybe also because anacondas prefer eau d’poisson over body odor. But could an anaconda occasionally eat a human?

Who better to ask this question to than Dr. Jesus Rivas, who has been studying anacondas in the wild for 20 years? 

Jesus Rivas examines a large female anaconda.
Rivas says that there are no documented cases of anacondas eating humans, but that might be partly because anacondas, especially the big ones, tend to live in remote areas with few humans. However, he describes two cases in which his field assistants have been stalkedunsuccessfully, phew!by their study animals. It was even caught on camera:

An anaconda stalks a scientist in the Venezuelan Llanos.

One thing is for certain: anacondas eat big stuff. Rivas has witnessed them eating white-tailed deer and crocodilians.  

An anaconda swallows a caiman.

If your interest in anacondas is piqued, Rivas has written a book on them, coming out in 2013. In this book, he shares an account in which he himself was stalked by a 15-foot anaconda affectionately named Lina. 

Rivas, J. A. 2013. Natural history of the green anaconda:  Two decades disentangling the secrets of the world’s largest snake. Oxford University Press.

In the meantime, check out this video of a large female anaconda puking up a cow!

If anacondas are the heaviest snakes, what are the longest? Reticulated pythons from Southeast Asia take that trophy, uncontested. The longest recorded “retic” is about 33 feet—yes, that’s five or six people laid end to end. Burmese pythons and African rock pythons can exceed lengths of 20 feet and are also quite formidable predators. These python species along with a few others star in the smorgasbord of online images of snakes eating large prey items.

A python has eaten a sheep.
A non-native Burmese python in the Florida Everglades ate an American alligator. The likely story is that the meal was too large and killed the snake, then scavengers noshed open the snake's belly.

A python kills a cow.

An olive python fixes to eat a wallaby.

But, do pythons eat humans? Let’s start with rock pythons, which—despite their penchant for eating lots of birds and non-human mammals—definitely have been known to occasionally include a human in the picnic basket.

Wikipedia cites a number of fatal attacks, in which a rock python killed a person but didn’t end up eating them. In at least two cases, the pre-teen prey was too large to get down the hatch; in another case a farmer was dragged up a tree by a python and rescued when he managed to call for help on his cell phone. In a few cases, however, the python managed to gulp down the prize: a 10 year-old was swallowed in 2002 in South Africa, and in the 1970’s a Portugese soldier was found inside the stomach of a snake.

A rock python has eaten a very large meal (not a human, however) and become stuck in a fence.

A close-up of the fenced snake, just for the awesomeness of it.

I asked Dr. Graham Alexander of The University of the Witwatersrand in South Africa to tell me about any close encounters he’s had with rock pythons during about eight years of studying them in the wild. Dr. Alexander said that the largest thing he ever witnessed a python eat was an impala, but that spending time in the wild with these huge snakes could be unnerving: 

“After tracking pythons for many years and not experiencing anything like a predatory attack, I felt pretty confident that they just didn’t do it (and I told many people that pythons don’t attack people). However, that all changed towards the end of 2010 when I was tracking both pythons and Puff Adders. I had about 30 telemetered snakes going at one time and tracking took all the day light hours – and I was often pretty rushed trying to get to all the snakes in a day. On three separate occasions in that season I was bitten on the leg by large female pythons that were lying in ambush. In these cases I had been pretty sloppy – moving in on the signal way too fast under time stress and probably with less caution than I should have – and accidently walked past the snake. My interpretation was that the pythons had struck and bitten me because they thought I was a meal. In only one of these cases did the python start trying to constrict, but even this one released me as soon as it realized that I was not an impala – or that’s how it seemed. In the other two cases, the python bit and released immediately without initiating constriction. In all three instances I was on my own and got the fright of my life. The bite comes out of nowhere and really does take you by surprise. I can really imagine what it is like for a real prey item. And that probably gives the snake a very large advantage.

I am afraid that those are the only experiences that could possibly be predatory attacks. I still think that we are not really on the menu of Southern African Pythons, though they do get pretty large and do consume meals of up to about 50 kg.”

A rock python has swallowed a prey item much larger than the width of its head.
Last but not least—let’s look into the maw of the star of the show, the retic.

Reticulated pythons, the longest species of snake alive, have munched on theirshare of people. Wikipedia lists a few instances of people being eaten by retics, some confirmed, some not: several people walking through the Malaysian bush got nabbed by 20+ foot pythons, including a Burmese jeweler in the early 1900’s who was eaten feet-first; plus a number of captive retics along with Burmese pythons have decided to eat their owners or their owners’ children.

The fact that it is the longest species alive today isn’t the only reason the reticulated python has notoriety among man-eating snakes. It holds the distinction of having had its man-eating tendencies studied thoroughly by an interdisciplinary team of scientists. A herpetologist (Harry Greene) got together with an anthropologist (Thomas Headland) and they found stuff out about man-eating snakes, stuff that neither would have been able to totally figure out on their own.  Awesome. 

Thomas N. Headland and Harry W. Greene. 2011. Hunter–gatherers and other primates as prey, predators, and competitors of snakes. Proceedings of the National Academy of Sciences of the USA 108:E1470-E1474. 

They studied the Agta Negritas, a tribe that was still pre-literate in the Philippines as of the 1970’s. The Agta hunted reticulated pythons for their meat, netting 25kg+ of meat per snake.

Agta Negrita hunters in the Philippines pose with a 20+ foot-long reticulated python in 1970.
But the hunter often became the hunted. From in-depth interviews with the Agta, the scientists discovered that large pythons had indeed tried (and sometimes succeeded) to eat tribe members. Over a period of time extending from the 1920’s through the 1970’s, the Agta reported 18 men that were unsuccessfully attacked by pythons, and six people that were killed by pythons.

So there you have it. Those are the records that we have of man-eating snakes in modern and ancient times. The numbers are small and the photos are few. 

This is the point where I should hear some of you calling bullshit. What’s that you say? You’ve seen photos online of giant snakes eating people?  

Take this photo of a large retic with a human-sized bulge captured in southeast Asia. Is this real?
Drumroll… Yes it is! But… that’s no human in the belly. This photo is often accompanied by the image below, allegedly showing the unlucky teenage boy cut from the snake’s guts.

A reticulated python has noshed a teenage boy… or has it really?

Except that the two snakes are clearly different animals. Whoops. I mean, who’s gonna notice a paltry detail like that when faced with a human body being cut from a snake’s stomach? 

Anyway, the question comes down to this: is this photo real? 

Killer photo opp. You can tell the photo is faked because the boy's body is not covered in digestive goo, but also because of the presence of the large bag or piece of fabric between the boy's head and the snake's guts. 
I'm not sure which is more awesome, thougha freshly ingested human body being cut from the belly of a retic, or a kid with enough cajones to stick his head and torso inside a dead snake's belly. 

I’ve saved the best for last. Here is a photo of one of the few allegedly real instances documented by photo in which a snake killed a human.

This unfortunate soul was killed by a reticulated python, but then the story goes that the meal was too big for the snake to take down—gobs of goo covered the man’s head but the snake couldn’t make it past his broad shoulders.

So, could it happen to you? I've always thought it would be an interesting way to die. But our chances of being eaten by a giant snake, even when wading through a flooded plain in Venezuela or spelunking in the Philippines, are lower than the chances of being struck by lightning at the exact same time as winning Mega Millions. 

Your chances might be a little higher if you encountered one of the beasts below coiled in the crook of an ancient swamp tree. At over 40 feet in length and weighing in at over a ton, Titanoboa—recreated by the awesome people at the Smithsonian—would definitely have noshed a few humans.

Smithsonian visitors view a scale model of Titanoboa.

Good thing for us that we didn’t evolve for another 55 million years.

Author's note: If you can identify the photographer of any of these photos, have information about them, or have a good story or photos of a man-eating snake, please let me know ( I will update the blog post with new information.

Monday, April 2, 2012

Cover models

The snakes of Chimineas Ranch have made it onto the surface of the journal Brain, Behavior, and Evolution. Behold! It's just so beautiful.

Back cover text reads:
A male Northern Pacific rattlesnake (Crotalus o. oreganus, larger snake) is seen courting a female one day following experimental translocation away from this same female. The snake navigated back to this female in less than 24 hours from 225 meters away. Inset: Cresyl violet-stained cross-section through the telencephalon of an adult male that received experimental translocations in the field. The medial and dorsal cortices are clearly visible. Photo courtesy Matthew Holding.

The paper was published online a while back, but there's something about seeing the creatures and tissue on the cover that gives me a big shiver. This study was Chapter 1 of my former graduate student Matt's thesis. It's one of the best studies I have been a part of.

The paper can be downloaded here.

Saturday, March 10, 2012

Gators gators everywhere but not a snake in sight

I am in the South, people. Do you have any idea how long I have wanted to come here? For years. I want to see alligators. I want to see Eastern Diamondbacked rattlesnakes. I want to see cottonmouths.

I'm here! But I'm here in March! It's not herping season. I came not to herp, but to rub elbows with the best biology educators in the country. The people who learn how students learn. The people who work tirelessly to improve the experience of students in the biology classroom, and of those of us lucky enough to teach them. I am in great company.

And let me tell you, learning how to learn (and teach) is tough work. We have had talks, demos, sharathons, posters, and ridiculously amazing meals constantly since we've been here. Every so often I'll just start twitching, thinking about all those beautiful southern herps waiting outside the window of the Swanctuary (my fond name for our royalty-worthy hotel). Today, I twitched myself out of my seat and zoomed out during a short break, on a serious mission. Must. Find. Gators.

I immediately got lost in the labyrinth of chic bungalows, windy lanes, and golf courses in which the Swanctuary is situated. Then I saw him. A huge gator sitting along the fairway next to a pond.

As I stealthily sidled up to him for a better photo, I heard someone yelling to me that there were FOUR gators to see! As I looked around frantically, a golf ball whizzed through the air by my head, and realizing the error of my ways I slunk off the green before I was mauled by men with coiffed hair.

Having made my escape, I realized it was all about the ponds. I jogged over to the next pond, and lo! A beautiful wee gator was basking in the setting sun, complete with a testudinean entourage. Look people- this gator is smiling. Wide as can be. I agreed with him at that moment- life is damn good in the South.

And around the next bend, I find this fine fellow sitting in the shade. Come on over, I dare you.

As I was trying to take an artsy photo of him with the water in the background, another creature swam into view. Gatorland, USA!

Our interloper up close:

It may not be snake season. But it's gator season every day. Thank you, gators of beautiful South Carolina, for welcoming me to your beautiful state.