Nonlinear material behaviour of spider silk yields robust webs

Although spider silk is used by spiders for many purposes, from wrapping prey to lining retreats22, 23, here we focus on silk’s structural role in aerial webs and on how silk’s material properties relate to web function. The mechanical behaviour of silk, like that of other biological materials, is determined by the nature of its constituent molecules and their hierarchical assembly into fibres13, 16, 17, 24, 25, 26 (Supplementary Fig. 1). Spider webs themselves are characterized by a highly organized geometry that optimizes their function7, 8, 18, 19, 20. To explore the contribution of the material characteristics to web function, we developed a web model with spiral and radial threads based on the geometry commonly found in orb webs1. The silk material behaviour was parameterized from atomistic simulations of dragline silk from the species Nephila clavipes (model A)16, 17 (Fig. 1a, b) and validated against experiments10 (Methods Summary). Properties of silk can vary across evolutionary lineages by over 100% (refs 9, 27 and 28; Supplementary Information section 1), so we avoided species-specific silk properties and instead used a representative model to reflect the characteristic nonlinear stress–strain (σ–ε) behaviour of silk found in a web. The mechanical performance of individual silk threads has been previously investigated10, 12, 13, and is in agreement with our model in terms of tensile deformation behaviour.