How Do Gold and Silver Beetles Get Their Colour?

silver-beetleThe gold and silver beetles of Costa Rica look like jewels fit for royalty. But despite their blingy appearance, Chrysina beetles are actually made from the same stuff as dowdy cockroaches and spiders – chitin.

The difference is that the elytra, or hard forewings, are made up of layers that bend light waves to give the illusion of a metallic sheen. Some 70 layers of chitin are stacked in decreasing thicknesses, refracting light at each interface. The wings of the golden beetle reflect light in wavelengths larger than 515 nanometres – similar to the reflection spectra for actual metals – while the silver beetle’s wings reflect wavelengths in the entire visible range. It’s thought their dewy appearance helps to camouflage them among the wet leaves of the Costa Rican rainforests.