chitin exoskeleton is covered in iridescent green oval scales. These contain diamond-based crystal lattices oriented in all directions to give a brilliant green coloration that hardly varies with angle. The scales are effectively divided into pixels about a micrometre wide. Each such pixel is a single crystal and reflects light in a direction different from its neighbours. Selective mirrors to create interference effects are formed of micron-sized bowl-shaped pits lined with multiple layers of chitin in the wing scales of Papilio palinurus, the emerald swallowtail butterfly. These act as highly selective mirrors for two wavelengths of light. Yellow light is reflected directly from the centres of the pits; blue light is reflected twice by the sides of the pits. The combination appears green, but can be seen as an array of yellow spots surrounded by blue circles under a microscope. Crystal fibres, formed of hexagonal arrays of hollow nanofibres, create the bright iridescent colours of the bristles of Aphrodita, the sea mouse, a non-wormlike genus of marine annelids. The colours are aposematic, warning predators not to attack. The chitin walls of the hollow bristles form a hexagonal honeycomb-shaped photonic crystal; the hexagonal holes are 0.51 μm apart. The structure behaves optically as if it consisted of a stack of 88 diffraction gratings, making Aphrodita one of the most iridescent of marine organisms. Deformed matrices, consisting of randomly oriented nanochannels in a spongelike keratin matrix, create the diffuse non-iridescent blue colour of Ara ararauna, the blue-and-yellow macaw. Since the reflections are not all arranged in the same direction, the colours, while still magnificent, do not vary much with angle, so they are not iridescent. Spiral coils, formed of helicoidally stacked cellulose microfibrils, create Bragg reflection in the "marble berries" of the African herb Pollia condensata, resulting in the most intense blue coloration known in nature. The berry's surface has four layers of cells with thick walls, containing spirals of transparent cellulose spaced so as to allow constructive interference with blue light. Below these cells is a layer two or three cells thick containing dark brown tannins. Pollia produces a stronger colour than the wings of Morpho butterflies, and is one of the first instances of structural coloration known from any plant. Each cell has its own thickness of stacked fibres, making it reflect a different colour from its neighbours, and producing a pixellated or pointillist effect with different blues speckled with