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New Study Uncovers Why These Snakes Wiggle When They Fly

Science
New Study Uncovers Why These Snakes Wiggle When They Fly
The south Asian paradise tree snake can launch itself into the air and glide from one tree branch to another. Thai National Parks, CC by 2.0

Did you know that some snakes can fly?

The south Asian paradise tree snake (Chrysopelea paradisi) can launch itself into the air and glide from one tree branch to another. And when it does, it moves its body in waves in something known as aerial undulation. Scientists have long known how the snakes moved. But they didn't know why. Until now.


"In all these years, I think I've seen close to a thousand glides," Virginia Tech professor Jake Socha, who has studied snake flight for more than 20 years, said in a university press release. "It's still amazing to see every time. Seeing it in person, there's something a little different about it. It's shocking still. What exactly is this animal doing? Being able to answer the questions I've had since I was a graduate student, many, many years later, is incredibly satisfying."

What Socha wanted to find out was whether the snakes' aerial undulation served any purpose.

"All snakes undulate when they move. And so on the ground, on a tree, in the water, they are creating these side-to-side waves," Socha told NPR. "It's not crazy to think that when the snake jumps into the air, the snake goes, 'Hey, I'm a snake. I undulate. That's what I should be doing.'"

To answer the question, Socha and his team created the first continuous, accurate 3D mathematical model of paradise tree snakes mid-glide, Virginia Tech reported. The model allowed them for the first time to see what would happen if the snakes didn't wiggle when they flew.

"You can do things with the model that you can't do with the live animal," Socha explained to USA TODAY. "What we wanted to do with the live animal is tell it to stop undulating. Like, 'Hey, snake, stop undulating.' We could tell the model to do that."

The results, published in Nature Physics Monday, showed that the undulation really does serve a purpose—it keeps the snakes stable as they fly.

"When you turned the undulation off in the model, you see that you get really bad gliding performance," Socha told USA TODAY. "In fact, it tumbles out of the sky much more readily than when you have undulation."

In order to build their model, the researchers first had to capture the snakes in motion. To do this, they borrowed space and some techniques from the world of theater and film.

During May and June of 2015, they filmed the snakes in a black-box theater at Virginia Tech called the Cube, which also contains motion-capture cameras.

The Cube is home to a 23-camera motion capture system. Jake Socha


"I guarantee you they did not have flying snakes in mind when they designed this facility," Socha told USA TODAY.

While filming, they placed 11 to 17 pieces of reflective tape on the snakes' bodies, similar to the tape worn by actors doing motion capture performances in Hollywood movies, NPR explained. They measured more than 100 snake glides to create their model, according to the press release.

The snakes wore 11 to 17 infrared-reflective markers, which gave the team high-resolution data while still allowing the animals to move freely. Jake Socha

Filming the snakes also taught the researchers more about the mechanics of the snakes' motion. They discovered that the snakes moved both side to side and up and down.

"What really makes this study powerful is that we were able to dramatically advance both our understanding of glide kinematics and our ability to model the system," lead author and recent Virginia Tech doctoral graduate Isaac Yeaton explained in the press release. "Snake flight is complicated, and it's often tricky to get the snakes to cooperate. And there are many intricacies to make the computational model accurate. But it's satisfying to put all of the pieces together."


A net-casting ogre-faced spider. CBG Photography Group, Centre for Biodiversity Genomics / CC BY-SA 3.0

Just in time for Halloween, scientists at Cornell University have published some frightening research, especially if you're an insect!

The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.

"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."

The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.

They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.

They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.

But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.

"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.

What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.

It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.

To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.

First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.

Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.

University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.

"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."

Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.

Hoy agreed.

"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.

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