Snake walk: The physics of slithering (2024)

  • Published

Snake walk: The physics of slithering (1)

By Jonathan Webb

Science reporter, BBC News

"This is the Mojave shovel-nosed snake," says Perrin Schiebel as she hands me a 40cm reptile. It is vibrantly patterned, apparently harmless, and quickly wraps itself around my fingers.

"They're native to deserts of the American south-west. This is a full-grown adult."

Ms Schiebel is studying for a PhD in physics at the Georgia Institute of Technology in Atlanta, US. She has spent many months putting 10 of these snakes through their slippery paces in a sand-filled aquarium.

Why is a team of physicists playing with snakes in a custom-built sand pit? Because, I am told, the way they move is a marvel. (The snakes, not the physicists.)

Innumerable critters have evolved superb ways to scuttle and slither - or even burrow and "swim" - across the most unhelpful of terrains: those that flow.

If you've ever tried to walk up a sand dune, then you are familiar with the problem: unstable ground makes a mission out of locomotion. Now, imagine doing it on your belly.

"One of the things that's really interesting about snakes is that their entire body is, in this type of locomotion, in sliding contact with the ground," Ms Schiebel explains.

"So they have to be able to push off things in their terrain effectively, to overcome the fact that they've got these frictional drag forces on their stomach all the time."

And these denizens of the desert - including my new shovel-nosed friend - make it look easy.

In fact, as soon as this particular snake lands back in the glass tank, it vanishes.

"They can travel fairly substantial distances completely submerged," Ms Schiebel says. "We think this body shape is an adaptation to that."

Some of her colleagues have used X-rays to peer beneath the sand and study the snake's swimming, external in detail. But she is more interested in how they get around on the surface.

Ms Schiebel has "tens of thousands of frames" of high-speed video showing the shovel-nosed snake navigating the tank, both with and without obstacles.

"That's what I'm interested in - how they can use these this flowing sand and these obstacles, and push off them to travel."

All in the wave

This laboratory, external has sand-based experiments down to a fine art. For one thing, the snake is not slithering on any old sand.

"These are 300-micron (0.3mm) glass beads," says Ms Schiebel. "So it's sort of a laboratory physics version of desert sand. That's very similar to the size and composition in their natural habitat."

Also in the name of precision, a remarkable routine unfolds in between trials. A pump blasts air through a mesh beneath the sand, to "fluidise" it; the artificial dune bursts into roiling movement.

"If you want to do controlled, repeatable experiments… you need some way to control the initial state of the media.

"With a fluidised bed you're guaranteed that the entire bed will be in the exact same state. And it lets you control things like the compaction very precisely."

One thing these controlled experiments have revealed is a surprising simplicity in the snake's slither. It arranges its body into a very regular, flat "S" shape - no matter what.

"I've studied 10 of these snakes and they always make the same shape," Ms Schiebel says. "That was somewhat surprising. With their long body, they're very flexible - you can imagine they could make all sorts of shapes.

"But there's this very specific, stereotyped waveform that they all seem to use."

This observation was in stark contrast to what the team expected - which was, in short, tortuous complexity.

"What I've found... is that the snake is using a waveform that is beneficial for travelling quickly at the surface - and that all of these complex things, like the grains flowing away, or the tracks the snake makes, may not be important."

It also marks out the shovel-nosed snake as rather different from other species, which the team has observed adopting much more irregular, complicated shapes in footage from a nearby zoo.

Wiggle and wind

One such species with a famously baffling gait is the sidewinder rattlesnake. Another member of the lab, Henry Astley, has been unravelling its secrets for some time.

"Sidewinding is famously confusing," he tells me as we look through some videos of real and simulated sidewinders in action. "There's actually a saying in herpetology, that if you want to go mad, watch sidewinders."

I can see his point. The hypnotic ripples of movement that propel these snakes - sideways - flow up-and-down along their bodies, as well as side-to-side.

Image source, Thinkstock

"During sidewinding, portions of the snake are lifted and lowered cyclically, in order to allow them to lift themselves over the sand and place their body in a new location," Dr Astley explains.

Working with a lab at Carnegie Mellon University, external in Pittsburgh, he and colleagues have already unpicked how the sidewinder climbs steep, sandy slopes by copying its movement with a robotic replica.

"Sidewinders are fantastic at locomoting - they're the real deal, they've got sensory systems and brains and muscles. But with that come the consequences of behaviour; they do what they want to do.

"With the robot, we can program it to do what we want it to do."

Using a similar approach - combining video footage of real snakes at Zoo Atlanta, with the programmable Pittsburgh robot - Dr Astley recently reported, external, for the first time, how sidewinders turn corners. He discovered two contrasting techniques.

First, there is the lazy "differential" turn, which works much like a car.

"One side of snake - or one set of wheels on the car - moves further than the other, and as a result, the whole animal rotates and you get this large, gradual turn over many, many cycles," he says.

The second option is more of a handbrake turn: the snake instantly reverses its body wiggle and jack-knifes its overall progress by anywhere from 70 to 180 degrees.

"The key is that in differential turning, the sidewinder continues with its head on the left or the right, throughout the turn," Dr Astley says.

"However in reversals, they instantaneously switch from head-on-the-right to head-on-the-left, or vice versa, allowing them to rapidly change and take off in a whole new direction."

Better bots?

When the team applied these findings to the sidewinder robot, which is ultimately aimed at search-and-rescue missions in tricky terrains, they managed to navigate a small maze with a combination of these turns.

But the research is not all about building better robots - though negotiating sandy landscapes will be crucial, for example, as humans continue to explore Mars.

Dan Goldman, who runs the lab at Georgia Tech, says he is most powerfully driven by pure intellectual curiosity.

"I'm interested in how nature works, in how living systems manage to do such beautiful and seemingly elegant behaviours in their natural environments."

The robots fill a gap, Prof Goldman explains, between mathematical simulations and real-world animal actions. Both the animals themselves and natural terrain - from leaf litter to sand dunes - are difficult to model accurately with computers.

"We don't have all the mathematics. There's a lot of parameters and it's also not clear how the biological subsystems are put together to effect interesting locomotor feats."

So a robot is a "physical model" that recreates certain elements of the interaction, in a programmable way.

"It's certainly not a faithful reproduction of an organism - but at least the leg of a robot, or the body of a snake robot, is interacting with a somewhat realistic material."

And therein, Prof Goldman concludes, lies a fruitful two-way street between his team of biology-focused physicists and the robotics engineers with whom they collaborate.

"It just turns out that the animals we study, and the physics we study... turn out to have some relevance for making better robots."

He and nearly 10,000 other physicists will be presenting their latest findings next week as the 2016 March Meeting, external of the American Physical Society.

You can hear an interview with Perrin Schiebel on Thursday's BBC Inside Science on Radio 4, or Science in Action on the BBC World Service.

Follow Jonathan on Twitter, external

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Snake walk: The physics of slithering (2024)


Snake walk: The physics of slithering? ›

Terrestrial snakes propel themselves by using a variety of techniques, including slithering by lateral undulation

lateral undulation
Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward. Examples of this type of gait include crawling in snakes, or swimming in the lamprey. › wiki › Undulatory_locomotion
of the body, rectilinear progression by unilateral contraction/extension of their belly, concertina-like motion by folding the body as the pleats of an accordion, and sidewinding motion by throwing the body ...

What are the mechanics of slithering? ›

We show that snakes use two principal mechanisms to slither on flat surfaces. First, their bellies are covered with scales that catch upon ground asperities, providing frictional anisotropy. Second, they are able to lift parts of their body slightly off the ground when moving.

Do snakes walk or slither? ›

Snakes do not have limbs. They move by dragging their body throughout in the form of loops. Hence, snakes have a crawling or slithering type of movement.

What is the mechanism of snake movement? ›

The serpent advances like a wave, through a sinusoidal movement of its body. Concertina or accordion: the snake forms volutes or twists with its body contracting and expanding successively like a spring or accordion, moving from one anchor or impulse point to the next.

How do snakes move in physics? ›

Overlapping belly scales provide friction with the ground that gives snakes a preferred direction of motion, like the motion of wheels or ice skates. Like wheels and ice skates, sliding forward for snakes takes less work than sliding sideways.

Why do snakes not slither straight? ›

Due to its long body it makes many loops and each loop gives the forward push, making snakes move forward very fast and not in a straight line.

What movement of it is called slithering? ›

When the snake moves, it makes many loops on its sides. The forward push of the loops against the surface makes the snake move forward. Movement of snake is called slithering movement.

What is the mechanics of movement? ›

Body movements involve force, balance, gravity and motion. “Biomechanics is effectively applying the physics of mechanics to problems in biology and medicine,” Weiss says. The main moving parts of your body include the solid bones, the joint tissues that link bones together, and the muscles that attach to your bones.

Do scientists know how snakes move? ›

Slithering, called serpentine locomotion, is dependent on the muscles that connect a snake's skin, spine, and hundreds of ribs and contract to form that familiar S shape. Snakes use friction with small bumps or uneven surfaces on the ground in order to propel forward.

Why do snakes slither sideways? ›

Previous studies have hypothesized that sidewinding may allow a snake to move better on sandy slopes. “The thought is that sidewinders spread out the forces that their bodies impart to the ground as they move so that they don't cause a sand dune to avalanche as they move across it,” Rieser explains.

What is unique about the movement of a snake? ›

Snakes do not have limbs. Instead, they have very flexible ribs, vertebrae and also their body has layers of muscles beneath the skin. These muscles contract and relax alternatively forming a wave-like motion. This type of movement is called slithering.

What are the three types of snake movements? ›

It is one of at least five forms of locomotion used by snakes, the others being lateral undulation, sidewinding, concertina movement, and slide-pushing. Unlike all other modes of snake locomotion, which include the snake bending its body, the snake flexes its body only when turning in rectilinear locomotion.

What is the pattern of snake movement? ›

Snakes will push off of any bump or other surface, rocks, trees, etc., to get going. They move in a wavy motion. They would not be able to move over slick surfaces like glass at all. This movement is also known as lateral undulation.

What is the movement pattern of a snake? ›

For several decades different types of snake locomotion have been categorized as one of four major modes: rectilinear, lateral undulation, sidewinding, and concertina.

How do snakes slither up walls? ›

They've got grooves and ridges along which the snake can anchor itself. Similarly, if the wall in question is a brick-layered wall, it would have grooves built into it. This makes it easy for a snake to slither along the uneven surface.

How did the snake slither? ›

A snake's ability to slither across the ground is made possible by its ability to bend using a series of muscles along their body. The scientific term for this bending motion is lateral and vertical bending. A snake uses lateral bending to change direction or propel itself forward along a flat surface.

Does a snake glide or crawl? ›

Note:Snakes do not have limbs so they cannot walk like other higher animals. They can crawl. Their movements rely on the scales and muscles.

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