Spider capture silk is a biomaterial with both high strength and high elasticity, but the structural design principle underlying these remarkable properties is still unknown. It was revealed recently by atomic force microscopy that, an exponential force--extension relationship holds both for capture silk mesostructures and for intact capture silk fibers [N. Becker et al., Nature Materials 2, 278 (2003)]. In this Letter a simple hierarchical chain model was proposed to understand and reproduce

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... is striking observation. In the hierarchical chain model, a polymer is composed of many structural motifs which organize into structural modules and supra-modules in a hierarchical manner. Each module in this hierarchy has its own characteristic force. The repetitive patterns in the amino acid sequence of the major flagelliform protein of spider capture silk is in support of this model.