Many animals, such as squid and chameleons, alter their colours by changing the size of pigment-carrying cells, but the Panamanian golden tortoise beetle Charidotella egregia has a completely novel way of going from metallic gold to matt red. Jean Pol Vigneron and colleagues from the University of Namur in Belgium have found that the beetle has a layered shell, and that each layer reflects a different colour and bears patches of nanoscale grooves.
This particular beetle normally has body fluid between these layers, filling the grooves and giving rise to mirror-like reflections that result in the insect's metallic gold appearance. When the fluid is withdrawn, the mirror-like effect disappears and the layers act as windows, displaying the red pigment below. This is an entirely novel mechanism for the control of colour and has the potential to give rise to innovative new display technologies.