On the colours of spider orb-webs

Suhr, Wilfried; Schlichting, H. Joachim. In: Eur. J. Phys. 32 (2011) 615 – 624

A sticky capture thread from the spiral element of spider orb-webs is formed of almost regularly spaced droplets that surround a supporting axial fibre. From the perspective of physical optics it represents a periodic linear array of scattering elements that acts as a diffraction grating. This is a novel aspect, which is of vital importance for the understanding of the overall scattering pattern. To demonstrate ist significance, we present our experimental findings and compare them with results of a simplified model.

The everyday life-world certainly is one of the most challenging contexts for the nontrivial application of fundamental physical principles. Many of its phenomena, discoverable by an experienced eye, have not yet been fully understood from a physical point of view. One of these only partially described phenomena is the colours of spider webs, of which Livingston stated in a 2005 article on ‘colour and light in nature’ that ‘a full explanation . . . has not yet been given . . . ’. This paper aims to open an approach to the physical origin of these colours
experimentally and theoretically. In view of their applicability in educational contexts, the experiments are performed with simple equipment, so that high-school and college students may reproduce them and understand the underlying physics.

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