How snakes traverse large obstacles in complex 3-D terrain

Snakes can traverse complex 3-D terrain by deforming their elongate body. Most previous studies on terrestrial snake locomotion focused on flat surfaces and planar gaits except for sidewinding with small body lifting. How snakes deform their body in 3-D to traverse complex 3-D terrain with large obstacles was less understood. We recently discovered that snakes use vertical undulation to traverse a horizontal ladder (Jurestovsky et al., in prep) and use lateral oscillation and vertical bending to traverse a large step (Gart, Mitchel, Li, 2020, JEB). Here, we hypothesized that vertical body bending is important for traversal of more complex rubble-like terrain and tested it using the generalist corn snake P. guttatus (N = 2 animals, n = 23 trials). The animal moved in a virtual tube, with little slip was observed where the body contacted the terrain despite low surface friction. The animal tended to move through lower valleys and mainly used vertical body bending to push against horizontal ridges. This was only occasionally complemented by lateral pushing against vertical walls. These observations supported our hypothesis. We plan to further study distributed contact forces using a sensorized snake robot as a physical model (see talk by Ramesh et al. in Robophysics sessions).