How snakes slither

The physics behind the snake’s slither has provoked much debate. Previous analyses suggested that snakes push against objects to propel themselves forward. This assumption has driven the design of search-and-rescue robotic snakes with wheels that go back and forth but not sideways. David Hu et al. propose that friction caused by the snake’s belly scales plays a critical role in movement. The authors focused on ‘‘lateral undulation,’’ a form of locomotion in which snakes apply lateral pressure against rocks and branches to move forward. To test their hypothesis, the authors used 10 juvenile pueblan milk snakes (Lampropeltis triangulum campbelli) and tested the sliding ability of the snakes covered in a cloth of similar thickness and roughness to their belly scales, and when they were covered in a slicker fiberboard. The authors also measured the snakes’ ability to move on surfaces covered with the same 2 materials. After measuring the snakes’ friction coefficients while slithering, the authors showed that the scales perform a vital function: they snag on rough surfaces and increase the resistance, which the snake uses for propulsion. — B.P.T.