The next generation of bank notes could make use of a security feature based on a novel characteristic of butterfly wings - a surface covered by a microscopic set of grooves that are finer than the wavelength of light.
The array of ridges and ribs on the butterfly wing allows the surface to generate colours without pigments. Swiss physicist Michael Gale has been developing ways of manufacturing this array for use on credit card and bank notes.
Speaking at a physics conference at Bath University he said the effect is similar to holograms used on credit cards but with several advantages. "It is more difficult to forge, and it shows well-defined colour changes if you rock the card from side to side or rotate it. It also works well in poor light," he said.