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Physics applies to animals in action over a wide range of spatial scales. At the smallest end of the range, attractive forces between nearby atoms facilitate the ability of geckos and some insects to climb up walls or even walk on ceilings. On a slightly larger scale, textures and structures provide adhesion for other biological gymnastics. In bird feathers, for instance, tiny hooks and barbs act like Velcro, holding feathers in position to enhance lift when flying, Rieser and colleagues report.
Biological textures also aid movement by facilitating friction between animal parts and surfaces. Scales on California king snakes possess textures that allow rapid forward sliding, but increase friction to retard backward or sideways motion. Some sidewinding snakes have apparently evolved different textures that reduce friction in the direction of motion, recent research suggests.
Small-scale structures are also important for animals’ interaction with water. For many animals, microstructures make the body “superhydrophobic” — capable of blocking the penetration of water. “In wet climates, water droplet shedding can be essential in animals, like flying birds and insects, where weight and stability are crucially important,” note Rieser, of Emory University, and coauthors Chantal Nguyen, Orit Peleg and Calvin Riiska.
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