Scattering
The orb web is horizontal and lit by sunlight in one area only. The colours are due to forward scattering (the sun was directly in front of the camera and about 10 degrees above the plane of the web. Typical sticky horizontal strands of web are covered with a glue that collects in tiny droplets some 5-10 microns in diameter. Wavelength dependent interference and diffraction as the scattered sunlight recombines produces the colours: more pronounced in slightly out of focus images as here. Colours in one particular direction vary as the spacings of semi-regular lines of droplets vary along the threads.
Scattering
The orb web is horizontal and lit by sunlight in one area only. The colours are due to forward scattering (the sun was directly in front of the camera and about 10 degrees above the plane of the web. Typical sticky horizontal strands of web are covered with a glue that collects in tiny droplets some 5-10 microns in diameter. Wavelength dependent interference and diffraction as the scattered sunlight recombines produces the colours: more pronounced in slightly out of focus images as here. Colours in one particular direction vary as the spacings of semi-regular lines of droplets vary along the threads.