Physics Of SnakeskinSheds Light On Sidewinding

Press release from Emory University:

Emory University | February 1, 2021

Most snakes get from A to B by bending their bodies into S-shapes and slithering forward headfirst. A few species, however — found in the deserts of North America, Africa and the Middle East — have an odder way of getting around. Known as “sidewinders,” these snakes lead with their mid-sections instead of their heads, slinking sideways across loose sand.

Scientists took a microscopic look at the skin of sidewinders to see if it plays a role in their unique method of movement. They discovered that sidewinders’ bellies are studded with tiny pits and have few, if any, of the tiny spikes found on the bellies of other snakes.

The Proceedings of the National Academy of Sciences (PNAS) published the discovery, which includes a mathematical model linking these distinct structures to function.

“The specialized locomotion of sidewinders evolved independently in different species in different parts of the world, suggesting that sidewinding is a good solution to a problem,” says Jennifer Rieser, assistant professor of physics at Emory University and a first author of the study. “Understanding how and why this example of convergent evolution works may allow us to adapt it for our own needs, such as building robots that can move in challenging environments.”

The Mexican lance-headed rattlesnake (Crotalus polystictus) moves by slithering forward. A micrograph from the study, above, of the skin of its belly reveals spikes that are normally invisible to the eye. The micrograph image shows a surface 20 microns wide, or about a third of the width of a human hair. (Tai-De Li)

The Mexican lance-headed rattlesnake (Crotalus polystictus) moves by slithering forward. A micrograph from the study, above, of the skin of its belly reveals spikes that are normally invisible to the eye. The micrograph image shows a surface 20 microns wide, or about a third of the width of a human hair. (Tai-De Li)

A micrograph of the skin of the Saharan sand viper (Cerastes vipera), a sidewinder, reveals that its belly is studded with pits instead of spikes. Image shows a surface about 20 microns wide. (Tai-De Li)

A micrograph of the skin of the Saharan sand viper (Cerastes vipera), a sidewinder, reveals that its belly is studded with pits instead of spikes. Image shows a surface about 20 microns wide. (Tai-De Li)

Co-authors of the paper include Joseph Mendelson, a herpetologist and the director of research at Zoo Atlanta; evolutionary biologist Jessica Tingle (University of California, Riverside); and physicists Daniel Goldman (Georgia Tech) and co-first author Tai-De Li (City University of New York).

Rieser’s research interests bring together the physics of soft matter — flowable materials like sand — and organismal biology. She studies how animals’ surfaces interact with the flowable materials in their environments to get around. Insights from her research may lead to improvements in human technology.

Snakes, and other limbless locomotors, are particularly interesting to Rieser. “Even though snakes have a relatively simple body plan, they are able to navigate a variety of habitats successfully,” she says. Their long, flexible bodies are inspiring work on “snake” robots for everything from surgical procedures to search-and-rescue missions in collapsed buildings, she adds.

In a previous paper, Rieser and colleagues found that designing robots to move in serpentine ways may help them to avoid catastrophe when they collide with objects in their path.

Sidewinders offered her a chance to dig further into how nature has evolved ways to move across loose sand and other soft matter.

This press release was produced by Emory University. The views expressed here are the author’s own.