Snakes on an inclined plane control scales to climb

Whether a serpent tempted Eve to eat apples from the Tree of Knowledge is up for debate, but now we understand better how it could have climbed the tree in the first place. It seems snakes can control each of their scales individually to grip rough surfaces and fight gravity.

Biologists have long known that snakes' scales are good for gripping. Their scallop-shaped geometry and the way they lie over each other like Venetian blinds help stop them sliding backwards.

Now Hamid Marvi of the Georgia Institute of Technology in Atlanta and colleagues have found that snakes can also control each scale. "[Biologists] knew about the passive mechanism, not the active one," he says.

"I'm not aware of previous published research showing active control of individual scales," agrees zoologist Harry Greene of Cornell University in Ithaca, New York.

Marvi and fellow researchers sedated an albino corn snake and let it slip, unconscious, down a ramp. They measured the angle at which they had to tilt the ramp to get the snake to slide, which revealed the coefficient of friction between the snake and the ramp.

Awake snake

They repeated the experiment with an alert snake and found that the coefficient of friction was twice as large as when it was asleep. That suggested it could do something to improve its grip.

"When the snake is unconscious, there is no control, no feedback, no sensory system," Marvi said at a press briefing at this week's American Physical Society conference in Boston. "But when the snake is conscious it can sense, 'I'm sliding, so I should do something.' There's an active mechanism involved."

Indeed, when the team took close-up videos of the snakes' soft underbellies, they found the snakes can control the angle of each scale to most effectively stick to a surface. "By controlling the initial angle of attack of the scale, snakes can increase their friction," Marvi says.

Armed with this knowledge, Marvi and colleagues built a climbing robot called Scalybot, which could be used for search and rescue work, he suggests.

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