The effects of surface feature geometry on the propulsive locomotion of tree-climbing snakes

Being limbless, snakes face unique challenges when climbing trees, sometimes resorting to  wrapping their bodies around the trunk to pull themselves up. However, corn snakes exhibit an alternative climbing technique that allows them to zig-zag up and down trees without wrapping. We model a large tree using a flat, vertical wall that utilizes a single vertical column of force sensors to record horizontal and vertical propulsive-force measurements as the snakes ascend or descend. This study investigates the force output over the body of the snakes through the combination of 3D-kinematic tracking data as well as time-resolved force data. Our findings reveal that the geometry and length of the pegs alters the snakes’ ability to climb. When the pegs were either shorter or narrower on the tip, snakes were less successful, meaning they were unable to complete the climb. In these scenarios, we saw reduced vertical forces applied to the pegs, indicating difficulty gripping the features, resulting in a higher chance of falling off the wall. In addition, we saw less horizontal force, crucial for stabilization, applied by the middle of the body. Conversely, snakes were more successful when the ends of the pegs were wider, as they could be used to generate greater stabilizing and supporting forces. In successful downward climbs, snakes anchored themselves by exerting more vertical forces with the tail. Future work will investigate how different snake species manage similar scenarios with different surface geometry.