Wildlife

Mystery Solved: How Snakes Climb Trees

Photo of a boa constrictor on a tree branch.
A boa constrictor crawls along a tree branch. Photograph by Pete Oxford, Minden Pictures/Corbis

When climbing a tree, a snake thinks “safety first,” according to new research published Tuesday in Biology Letters. 

Instead of gripping the tree with just enough force to keep from sliding back down, snakes overcompensate and grip with a force that far exceeds what’s necessary. Researchers think that in doing this, snakes are choosing between getting up the tree more easily and decreasing their risk of falling.

Greg Byrnes, a herpetologist at Siena College in New York and lead author of the paper, realized that although scientists knew that snakes climbed trees and had a rough idea how they did it, no one knew exactly how much force the snakes generated to climb or how they determined how much force to use. Byrnes set out to solve that mystery and was surprised by what he found.

“For a snake, being safe is way, way more important than being cost-effective,” he said.

Climbing vertically isn’t easy, as anyone who has climbed a rope in gym class can attest. Reaching new heights requires a lot of energy. Still, for plenty of animals, climbing is well worth the cost. For snakes, some of which are arboreal species and spend most of their time in trees, it can be a way both to escape predators and to catch their prey. (See “How Geckos Turn Their Stickiness On and Off.”)

How an animal climbs a tree depends on its physical features. Cats, for example, can grip a tree with their claws, which helps make climbing easier. Humans have to rely on muscle strength to exert enough force to keep from falling. Although snakes don’t have limbs, they also use muscular force to climb trees, which they create by firmly wrapping their bodies around the trunk of a tree.

Byrnes and colleague Bruce Jayne at the University of Cincinnati measured grip strength in the lab by building a 94.4-inch-tall (240 centimeters) cylinder to act as a tree trunk. They placed pressure sensors on various parts of the “trunk” and wrapped it with a textured tape. They filmed the process as five different species of snake climbed the “tree.” Some of the species, such as Morelia nauta, live almost their entire lives in trees. Others, such as Boa constrictor, spend a lot of time in trees as juveniles to hide from predators, but then come down as adults. (See also “Brazilian Investigators Crack the Case of the Missing One-of-a-Kind Snake.”)

Because snake bodies are long and thin, the animals could wrap themselves around the artificial tree trunk in a variety of orientations, from wrapping evenly around the trunk to bunching most of their body at one height. However the snakes did it, Byrnes and Jayne found that all five species used far more force than was strictly necessary to keep their bodies from sliding back down—sometimes almost three times as much, the researchers report.

Byrnes believes that this extra-strong grip, which requires extra energy, benefits the snake by decreasing its chances of falling. The dangers of a fall, Byrnes says, are less about direct physical harm and more about exposure.

“A ten-meter fall is unlikely to really hurt a snake, but being back on the ground could expose them to predators. Then the snake will have to climb the tree again, and it might be more energy efficient to be more careful the first time,” Byrnes said.

Byrnes believes that strategies to prevent falling are the rule in the animal kingdom, rather than the exception. So the next time your arms start shaking as you climb that rope in gym class, remember that your muscles are fighting the age-old battle to stay safe at great heights.

Follow Carrie Arnold on Twitter and Google+.

Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at http://www.carriearnold.com
  • Tom

    Animals have no health care in the wild if injured so self preservation is paramount.

  • jim adams

    30 -40 years ago i watched a black snake climb a black oak tree. The tree was between 1 1/2 to 2 feet in diameter and probably 60 feet tall. It was a forest tree with a long, bare trunk and all it’s branches up where there was enough light for photosynthesis. Large black oaks have a corrugated bark which channels water very nicely during heavy rains.

    The snake was 3 to 4 feet long. And it went straight up the tree, fitting itself in between the corrugations of bark. Snake scales — stomach and sides — have unattached edges facing backwards which braces the snake as it wriggles and stretches it’s way up the tree. I lost sight of it about 15 or so feet tho i no longer remember why.

    A cat which climbs with it’s one way claws is somewhat similar to a snake, holding itself head up/tail down during it’s climb. The cat of course must climb down backwards, still with head up and tail down for it’s claws to work

    I don’t know how a snake gets down tho i doubt it is by backing down the tree like a cat. And i’m starting to appreciate how the SE Asian flying snakes evolved. Black snakes can flatten themselves to an extent — and i suspect that it can stablize it’s fall by doing so and S-curving itself for added balance. Probably in much the same way a cat or squirrel can stabilize themselves and fall long distances with out hurt on landing

    My wife tells me she has seen black snakes climb in the same way — straight up the tree, braces against the corrugations.

    Is there any way of Dr Brynes checking in on this? Doing senior science surveys on line? Thanks

  • Konie Smalls

    My husband was relaxing on our back sun porch when I saw him squinting. What is it I asked but he didn’t say anything. He just got up grabbed a hoe and proceeded to start chopping at an old pecan tree. All of a sudden this large 5.6ft grey snake uncoils and falls to the ground. I still can’t believe he saw that thing! It was almost the same color as the bark on the pecan tree! He’s my hero!

  • Just Wow

    @Konie Smalls … Wow. Your husband is a hero because he killed a snake in your yard? A snake that could eat mice and rats and has a natural place in wildlife? Wildlife deserves more respect. Unbelievable.

  • Rae Bowen

    I am completely phobic when it comes to snakes and anything that resembles them. I’ve never killed one though. I don’t even ask others to kill them. Despite my phobia I am aware of the roll they have in the environment. So I must say that your husband shouldn’t have killed the snake. Taken it to a preserve or elsewhere yes, killed no. It’s funny that this is coming from me because I’m so scared of snakes that upon seeing one in my yard I have to close my vents believing they will get in my house. When it rains I look like I’m playing hopscotch because I can’t bring myself to step on a worm (small snake). When faced with a snake ask someone to capture it and release it in the wild or at least 50 miles from my house.

  • Dale Vogel

    I’ve seen a black snake climb straight up the side of my house.

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