Natural Locomotion in Fluids and on Surfaces

Abstract

Limbless terrestrial animals propel themselves by sliding their bellies along the ground. Although the study of dry solid-solid friction is a classical subject, the mechanisms underlying friction-based limbless propulsion have received little attention. We review and expand upon our previous work on the locomotion of snakes, who are expert sliders. We show that snakes use two principal mechanisms to slither on flat surfaces. First, their bellies are covered with scales that catch upon ground asperities, providing frictional anisotropy. Second, they are able to lift parts of their body slightly off the ground when moving. This reduces undesired frictional drag and applies greater pressure to the parts of the belly that are pushing the snake forwards. We review a theoretical framework that may be adapted by future investigators to understand other kinds of limbless locomotion.