Brown Tree Snakes Use Key Muscles to “Stand” Upright — Possibly Inspiring Future Soft Robotics

Snakes use their many muscles to slither through grass, sand, and even water. But they can also use those muscles to stand.

In a feat that seems to bend the rules of physics, researchers have discovered what gives tree snakes the ability to lift 70 percent of their body length and “stand” almost straight up in the air.

Publishing their findings in the Journal of the Royal Society Interface, the team found that a combination of muscles, gravity, and proprioceptive feedback (perceived body position) helps this slithery snake reach for the skies. And, these new findings could help advance robotics.

Read More: 100 Million Years Ago, Snakes Gained Their Most Iconic Traits

Snakes that Can “Stand”

Snakes like the brown tree snake or the scrub python can lift almost all of their body vertically to help them get from branch to branch in a tree. This seems unlikely, as they don’t have limbs like many other animals do, and because their bodies can buckle under their own weight, as with many other animals.

This vertical ability puzzled reseachers, so to understand this impressive skill, the research team — led by L. Mahadevan, the Lola England de Valpine professor of Applied Mathematics, Physics, and Organismic and Evolutionary Biology in the John A. Paulson School of Engineering and Applied Sciences and the Faculty of Arts and Sciences — tracked snakes’ muscle movements and compared it to data collected from a 2017 Journal of Experimental Biology study.

For the experiment, all of the snakes were on a perch — similar to a tree branch. The team then closely monitored the snake’s movements as it rose vertically, attempting to move to a different perch. From their monitoring, the team noted one simple strategy. The snakes did not stiffen their entire bodies; instead, they tightened their muscles and created a slight bend near the base of the perch. This bend, according to the team, creates a sort of “boundary layer” in the snake.

From there, the snake propels most of its body vertically and stands almost perfectly straight, thereby preventing gravity from creating additional bending torque and reducing the energy needed to maintain its balance.

Key Muscles and a Slight Bend

To understand their observations, the team created a mathematical model that represents the snake as an active elastic filament — a soft structure capable of sensing its own shape and responding with muscle forces.

From the models, the researchers examined two control strategies. The first, local feedback, examines how the muscles respond to bending and stiffening the body. The second, optimal control, looks at how the muscles coordinate in a non-local way along the body to minimize energy use.

“For some it may be the stuff of nightmares, but we’ve now analyzed, mathematically and physically, the hidden physics and control strategies that allow snakes to defy gravity,” said Mahadevan, in a press release.

Snakes Inspiring Future Robotics

The study results revealed not only how snakes can keep themselves upright, but also that maintaining an upright posture is much harder than lifting their bodies into that position. According to the findings, only minimal muscle force is required to lift a snake’s body into an upright position; much more muscle force is required to maintain that posture.

This could explain why, along with the gentle bend in the snake’s lower body, it seems to sway slightly back and forth to keep its balance.

From this work, the research team hopes these abilities could one day be applied to soft robotics — flexible materials that can be used in medical advancements, as well as in space and underwater applications.

“By concentrating control where it counts, engineers may learn to build machines that are both efficient and resilient,” said first author Ludwig Hoffmann, a postdoctoral researcher in applied mathematics, in the press release.

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