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The small structures that decorate biological surfaces can significantly affect behavior, yet the diversity of animal–environment interactions essential for survival makes ascribing functions to structures challenging. Microscopic skin textures may be particularly important for snakes and other limbless locomotors, where substrate interactions are mediated solely through body contact. While previous studies have characterized ventral surface features of some snake species, the functional consequences of these textures are not fully understood. Here, we perform a comparative study, combining atomic force microscopy measurements with mathematical modeling to generate predictions that link microscopic textures to locomotor performance. We discover an evolutionary convergence in the ventral skin structures of a few sidewinding specialist vipers that inhabit sandy deserts—an isotropic texture that is distinct from the head-to-tail-oriented, micrometer-sized spikes observed on a phylogenetically broad sampling of nonsidewinding vipers and other snakes from diverse habitats and wide geographic range. A mathematical model that relates structural directionality to frictional anisotropy reveals that isotropy enhances movement during sidewinding, whereas anisotropy improves movement during slithering via lateral undulation of the body. Our results highlight how an integrated approach can provide quantitative predictions for structure–function relationships and insights into behavioral and evolutionary adaptations in biological systems. 

Water‐responsive (WR) materials that strongly swell and shrink in response to changes in relative humidity (RH) have shown a great potential to serve as high‐energy actuators for soft robotics and new energy‐harvesting systems. However, the design criteria governing the scalable and high‐efficiency WR actuation remain unclear, and thus inhibit further development of WR materials for practical applications. Nature has provided excellent examples of WR materials that contain stiff nanocrystalline structures that can be crucial to understand the fundamentals of WR behavior. This work reports that regeneratedBombyx (B.) morisilk can be processed to increase β‐sheet crystallinity, which dramatically increases the WR energy density to 1.6 MJ m⁻³, surpassing that of all known natural muscles, including mammalian muscles and insect muscles. Interestingly, the maximum water sorption decreases from 80.4% to 19.2% as the silk's β‐sheet crystallinity increases from 19.7% to 57.6%, but the silk's WR energy density shows an eightfold increase with higher fractions of β‐sheets. The findings of this study suggest that high crystallinity of silk reduces energy dissipation and translates the chemical potential of water‐induced pressure to external loads more efficiently during the hydration/dehydration processes. Moreover, the availability ofB. morisilk opens up possibilities for simple and scalable modification and production of powerful WR actuators.