The Slippery Secret of Snakes

October 23, 2015

A team from MPI-P and Oregon State University have discovered why the underbelly of the California King Snake is so slick and suitable for slithering -- a window onto an evolutionary adaptation that may inspire new types of water-resistant paints and plastics.

A shed skin of the California King Snake, examined in molecular detail by a team of researchers in Oregon and MPI-P, may have yielded one of the reptile's slippery secrets. Using a combination of techniques that allowed to explore how molecules are arranged on the surface of the scaly skin, the team discovered what may be an unprecedented evolutionary adaptation that allows the animal to reduce friction on its underbelly and slither smoothly over surfaces.

The work may inspire new types of paints, coatings, plastics and other materials that are resistant to water -- or ultra slippery surfaces for other applications like robotic drone snakes. Engineers have designed fully articulated snake-like robots that can wriggle and writhe just like the real thing in recent years, but they have trouble slithering over some surfaces because their movement creates too much friction.

Anyone who has felt the soft body of a real snake knows how slick they feel -- a tactile trait that arises from its slippery scales, which are themselves covered with a fatty "lipid" molecule the snake produces. But one puzzling feature of these scales is that they essentially do not vary in size and shape over the body of the snake and yet numerous laboratory measurements confirm that snakes are more slippery on the belly than along the spine -- even thought the scales look the same under a microscope.

Examining the surface of scales taken from both the belly and the back, the team found that the fatty lipid molecules on the reptile's underside line up like little soldiers, in tiny uniform rows and columns almost perpendicular to the surface. It is this orderly boundary layer of lubricant, the researchers say, which reduces friction for the California King Snake.

"It's crazy how well ordered the layer is," said Joe Baio, who led the research at Oregon State University. "It would be hard for me to believe it is random because you have to work hard to make a well-ordered monolayer."

Scientists have looked at the chemistry of snake scales before, but this was the first time anyone looked at them with techniques sensitive enough to detect the ordering of molecules on the surface. Baio's collaborator Stanislav Gorb at the University of Kiel in Germany provided the snake skin samples, and the work is part of a larger collaboration that aims to compare the surfaces of snake scales across species.

The new work suggests that controlled and ordered lipids molecules on their belly scales is another adaptation that makes it better at slithering -- and therefore hunting. Snake scales serve a number of purposes for the animal, including helping the cold-blooded creature regulate its temperature, providing camouflage and possibly regulating water retention.

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