Meeting Abstract
Elongate, legless organisms, such as snakes, seemingly use simple body undulations to move on and within deformable substrates like sand. Previously, we have gained insight into the response of granular media (GM) to subsurface intrusion and used this understanding to find principles of subsurface undulatory locomotion. However, our knowledge of the physics of GM at the surface is limited. Therefore, when we challenged a variety of snake species to travel across the surface of a GM we found that performance was widely variable–ranging from efficient movement to complete failure–without an immediately obvious connection between various locomotor strategies and success. To understand what factors contribute to successful locomotion on challenging GM substrates, we focused on the study of a desert-dwelling snake Chionactis occipitalis (the Mojave Shovel-nose snake). We collected high-speed video of Chionactis (N = 10) moving on ~0.3 mm glass particles (a similar size to the GM in its natural habitat) and digitized the snake body for analysis. Using the organism studies in combination with resistive force theory calculations, GM drag experiments, and tests of a physical model (a snake-like robot), we find several factors which, acting together, contribute to animal performance; the body kinematics—targeting an ideal waveform, the ability to lift portions off of the substrate, and the properties of the GM. Based on the sensitive nature of the relationship between these factors, we hypothesize that having an element of force-based control, where the waveform is modulated in response to the forces acting between the body and the environment, is necessary for successful locomotion on flowing, granular substrates.
