CREDIT card fraud could be prevented by picking up a tip from colourful
butterflies in Indonesia. The Papilio palinurus is the only butterfly
known to make its hues entirely mechanically, without any pigments.
By bouncing light around in microscopic bowl-shaped cavities on their wings,
butterflies appear lush green. 鈥淔rom the flat centre of each bowl, you get
yellow light reflected, and from the sloping sides, you get blue reflectivity,鈥�
explains Peter Vukusic, head of the team investigating the phenomenon at the
University of Exeter (Nature, vol 404, p 457). 鈥淭he eye can鈥檛
distinguish them and combines yellow and blue to form green,鈥� he says. Forgers
would find it difficult to repeat this trick, he says.