Research into the colouring of two Costa Rican beetles may hold the clue to how some animals recreate the glitter and lustre of silver and gold. Chrysina aurigans (gold) and Chrysina limbata (silver) were studied by researchers from the University of Costa Rica for clues as to their metallic brilliance.
The shiny back of the chrysina beetle is called the elytron and protects the delicate flight wing underneath. The elytron is formed by layers of chitin – a nitrogen-containing complex sugar that creates the hard outer skeletons of insects, crabs, shrimps, and lobsters.
The researchers found that the chitin – only a tenth of a millimetre thick – was layered from the bottom up in progessively thinner layers. This structure is described as “chirped”.
Each layer of chitin reflects some light and transmits the rest down to the next layer. Each portion of reflected light joins with reflected light of the same wavelength from other layers. This causes an amplification effect similar to the phenomenon of rogue waves or natural frequency – which smashes glass during an operatic performance.
It is this amplification which creates the brilliance and sheen associated with metallic objects.
Physicist and study leader William E. Vargas explains the impact of this finding:
“The detailed understanding of the mechanism used by the beetles to produce this metallic appearance opens the possibility to replicate the structure used to achieve it and thus produce materials that, for example, might look like gold or silver but are actually synthesized from organic media.”
The article, Visible light reflection spectra from cuticle layered materials by Cristian Campos-Fernández, Daniel E. Azofeifa, Marcela Hernández-Jiménez, Adams Ruiz-Ruiz and William E. Vargas appears in the journal Optical Materials Express.
