Figure 2.

Design spaces. (a) Mechanical design space contrasting friction (surface property) vs. stiffness (bulk property). Top left: spatula ends of adhesive setae (Cupiennius salei). Top right: C. salei tarsal claw. Bottom right: C. salei fang. Bottom left: the cuticular pad in C. salei acts as a high pass filter for surface vibration in front of the metatarsal lyriform slit organ. Center: sensory hairs (setae); variations in spring constant stiffness and damping properties determine the hairs' sensitivity. (b) Optical design space. The design space is depicted as a projection of a cone along its central axis. The tip of the cone (centre of the circle (i) represents transparent properties. It is represented by anti-reflective epi-cuticlar nano-structures, as found on the cornea of spiders. Three axes emerging from the tip are: absorption, directional and diffuse scattering. The structures discussed occupy different regions within the design space. (ii) In the spider P. rubroargentea, the spiny cuticular extensions contain melanin within the cuticle as well as in melanophores. (iii) Schematic of cross-section of the yellow hairs of P. metallica, showing short-range order cuticular/air domains. (iv) Morphology of the yellow hairs of P. metallica, microtrichs contribute to diffuse scattering. (v) Schematic of the scale of M. nigromaculatus: diffraction grating on a curved surface. (vi) Schematic of the scale of M. robinsoni: diffraction grating on a flat surface. (vii) Guanine platelet crystals in the tapetum of spider eyes. (viii) Schematic cross-section of the blue hairs of P. metallica, showing order cuticular/air lamina. Note that the distribution of the structures along the depth of the cone is lost in this representation. (Online version in colour.)