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Radial filament of the netcasting spider Asianopis subrufa, showing an elastomeric core encased by bundles of fine fibers.EVOLUTION Architecture of netcasting spider silk The design of polymers typically involves a trade-off between materials that are strong but brittle and materials that are elastic but lacking in strength.Spiders may overcome such inherent limitations by processing silk fibers into composite materials.Jonas Wolff et al. used high-speed videography and structural analyses to characterize the mechanical properties of webs spun by netcasting spiders (Deinopidae).Netcasting spiders capture prey with webs of sticky spider silk held by their anterior legs.During a predatory strike, the radii of the net reversibly undergo extreme elongations of up to 90-200%.In comparison, the web radii of orb-weaver spiders can only reversibly deform by 2-5% and fracture at elongations over 20%.The radii of the netcasting spiders' web were composed of an elastomeric core surrounded by looped bundles of fine fibers, produced through a reel-spinning technique.The fibers are initially compliant and highly extensible but stiffen as the loops straighten, enhancing the load-bearing capacity to hold prey.The spiders modify the structure of each radius and frame element to create an elasticity gradient across the web.According to the authors, the design principles of netcasting spiders could inspire the development of artificial materials with high elasticity and strength.-M.H.