  Limbless organisms such as snakes can navigate nearly all terrain. In
particular, desert-dwelling sidewinder rattlesnakes (Crotalus cerastes) operate
effectively on inclined granular media (such as sand dunes) that induce failure
in field-tested limbless robots through slipping and pitching. Our laboratory
experiments reveal that as granular incline angle increases, sidewinder
rattlesnakes increase the length of their body in contact with the sand.
Implementing this strategy in a physical robot model of the snake enables the
device to ascend sandy slopes close to the angle of maximum slope stability.
Plate drag experiments demonstrate that granular yield stresses decrease with
increasing incline angle. Together, these three approaches demonstrate how
sidewinding with contact-length control mitigates failure on granular media.
