Redundant contacts and force redistribution stabilize limbless vertical climbing
- 1Emory University
Abstract
Animals navigating complex vertical environments must secure stable footholds, a challenge for species without feet. While arboreal climbing has evolved repeatedly in snakes, the physical mechanisms they use to scale broad, nearly flat surfaces remain poorly understood. By measuring three-dimensional body kinematics and per-contact forces on a smooth vertical wall with protruding posts, we show that cornsnakes climb by dynamically balancing forces across a highly redundant network of 5 to 16 simultaneous contacts--far exceeding the three contacts minimally required for physical stability. Using a computational model and a robotic climber, we demonstrate that while simple body undulations and passive friction are mechanically sufficient to climb this terrain, snakes systematically deviate from this passive baseline. While downward climbing relies primarily on friction, ascending snakes actively generate positive mechanical work at their contacts to propel themselves. Furthermore, we found that whenever a snake engages a new contact, it triggers a stereotyped, system-wide redistribution of force that seamlessly integrates the new foothold without disrupting whole-body balance. These results reveal how a continuous, flexible body can transform sparse environmental features into a robust, fault-tolerant network. This mechanism provides a biomechanical framework for understanding the repeated evolution of limbless climbing and offers physical principles for designing agile robots for unstructured terrain.
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BibTeX
@misc{riiska2026redundant,
title = {{Redundant contacts and force redistribution stabilize limbless vertical climbing}},
author = {C. A. Riiska and M. Lee and Y. Nemenman and G. Thacker and J. R. Mendelson and J. M. Rieser},
howpublished = {bioRxiv},
year = {2026},
month = jul,
doi = {10.64898/2026.07.06.736779},
url = {https://www.biorxiv.org/content/10.64898/2026.07.06.736779v2},
note = {CC BY-NC},
}
RIS
TY - UNPB
TI - Redundant contacts and force redistribution stabilize limbless vertical climbing
AU - C. A. Riiska
AU - M. Lee
AU - Y. Nemenman
AU - G. Thacker
AU - J. R. Mendelson
AU - J. M. Rieser
PY - 2026
DA - 2026/07/06
PB - bioRxiv
DO - 10.64898/2026.07.06.736779
UR - https://www.biorxiv.org/content/10.64898/2026.07.06.736779v2
AB - Animals navigating complex vertical environments must secure stable footholds, a challenge for species without feet. While arboreal climbing has evolved repeatedly in snakes, the physical mechanisms they use to scale broad, nearly flat surfaces remain poorly understood. By measuring three-dimensional body kinematics and per-contact forces on a smooth vertical wall with protruding posts, we show that cornsnakes climb by dynamically balancing forces across a highly redundant network of 5 to 16 simultaneous contacts--far exceeding the three contacts minimally required for physical stability. Using a computational model and a robotic climber, we demonstrate that while simple body undulations and passive friction are mechanically sufficient to climb this terrain, snakes systematically deviate from this passive baseline. While downward climbing relies primarily on friction, ascending snakes actively generate positive mechanical work at their contacts to propel themselves. Furthermore, we found that whenever a snake engages a new contact, it triggers a stereotyped, system-wide redistribution of force that seamlessly integrates the new foothold without disrupting whole-body balance. These results reveal how a continuous, flexible body can transform sparse environmental features into a robust, fault-tolerant network. This mechanism provides a biomechanical framework for understanding the repeated evolution of limbless climbing and offers physical principles for designing agile robots for unstructured terrain.
ER -