For animals with no arms or legs, tree-dwelling snakes sure can get around.
Many species hoist themselves from branch to branch using what’s known as a “bridging” behaviour: The reptile will extend the front half of its body out into the air, like a cantilever, until it makes contact with something large enough to support its weight.
The five species of so-called flying snakes in the genus Chrysopelea, native to Asia, have an even cooler trick: They can flatten their bodies in midair and glide through the treetops like a flying squirrel, up to 91 metres at a time.
Now, there’s evidence that Australian snakes in the genus Dendrelaphis, which are closely related to Chrysopelea, can jump.
Watch a bronzeback snake, D. pictus, leaping between gaps in vegetation in Malaysia.
Eager to learn more, Graham traveled to Australia, where she temporarily captured some Dendrelaphis animals from the wild and coaxed them into performing their behaviours in a lab experiment, on a structure made out of PVC pipe, tree branches, and GoPro cameras.
“It’s basically a little snake jungle gym,” says Graham.
By investigating how snakes move around their environment, the scientists have revealed more insights into the diversity of animal locomotion, which has implications for how these bizarre behaviours may have evolved.
Snakes on a plane
Most of us take the fact that we live on a two-dimensional plane for granted. By and large, when you take a step forward, you can count on the ground being there to receive your foot.
But for animals living in the treetops, the world is a highly disconnected affair. Birds navigate this 3-D space by flying. Howler monkeys swing between branches. And sloths simply reach out and grab the next limb they want to travel to. But all of those behaviours require fancy appendages that snakes lack.
“What’s interesting about these snakes is their ability to do all these interesting locomotive behaviours with no limbs,” says Graham. (Read how scales are key to snake locomotion.)
Of course, getting the wild animals to perform those behaviours on the jungle gym was no easy task. The first tree snake Graham caught happened to be a rather large female, who was “not interested in doing this jumping behaviour at all.”
There are some high stakes acrobatics going on in the jungles of Indonesia.
But her persistence paid off, and after collecting numerous tree snakes of all shapes and sizes, Graham was able to confirm that snakes in the genus Dendrelaphis can, indeed, hurl themselves across a gap.
To do so, the snakes slink down below their target—say, a tree branch—and then launch themselves upward in a way that their momentum carries them across the gap. Graham plans to publish more details about her research in two scientific papers in 2020.
Leaps for lulz?
Now that Graham has confirmed that these tree snakes can jump, she wants to know why they do it.
This may seem like common sense, but Graham says that there’s really no good evidence yet as to why any gliding animals do what they do. Some scientists have hypothesised that jumping or gliding saves snakes, squirrels, or lizards time or energy, but there are “no supporting empirical studies” that prove it.
King cobras avoid humans, but when cornered they can deliver enough venom in their bite to kill 20 people. They can also move forward while looking a 6-foot-tall (1.8-metres-tall) person in the eye, a third of their body raised up off the ground. Found in India, southern China, and Southeast Asia, king cobras are the only snakes in the world to build nests for their eggs.
PHOTOGRAPH BY MATTIAS KLUM
“To be the first person studying this behaviour means you don’t really know the context in which a snake does it,” says Graham. Is jumping “an escape behaviour? Is it a common transport behaviour? Is it just something they do for lulz? Nobody knows, right?”
Bruce Jayne, a functional morphologist at the University of Cincinnati in Ohio, says Graham’s decision to study the close relatives of flying snakes is smart, because it could give us a better idea of how these jumping and gliding behaviours evolved. (Read about a venomous snake species discovered in Australia.)
“Really, how special is this ability in flying snakes?” says Jayne. “If we look at their close relatives, can we actually see some precedents for the behaviour. Maybe the flying snakes are just sort of at one end of the continuum.”
In any event, he says he admires the work, because he knows how tough it is to study these snakes in particular.
“It can be quite a roll of the dice when you do this stuff,” says Jayne. “But given the track record [with Socha’s lab], I think that if anyone can do it, that group can.”
Lead Image: A common tree snake in the genus Dendrelaphis basks in the sun between research trials.
PHOTOGRAPH BY JAKE SOCHA