The Gold and Silver Beetles of Costa Rica

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Imagine you're a conquistador in the 1500s. You've spent many weeks on a boat to get to Central America and many days hacking away through the jungle, dressed in hot and heavy armor, swatting at mosquitoes, desperately trying to find that fortune you were promised back home. Then you glimpse a bit of silver or gold. As you get closer, it scurries away, and you start to wonder just how crazy this trip is going to make you.

Costa Rica, rather lacking in actual gold and silver, is home to two beetle species that may have made a conquistador or two a little nuts: Chrysina aurigans, the gold variety, and C. limbata, in silver. Then again, maybe not, as the reflective surfaces likely provide good camouflage in the rainforest, where the light reflecting off them would look a lot like the light reflecting off wet leaves.

Materials scientists at the University of Costa Rica studied the light reflected off the 70 layers of chitin that form the bright forewings of these two species of beetle. (Their study appears in Optical Materials Express.) They found that a bit of light is reflected by each layer, and all those bits add up to make the reflected light brighter and brighter, giving the beetle its sheen and shine. The golden C. aurigans reflects light in wavelengths larger than 515 nm, which give it a redder color, while the silver C. limbata reflects wavelengths in the entire visible range (and as we know from elementary school, adding up all the colors of the rainbow results in a white light).

The researchers say that learning more about how the beetles mimic metallic surfaces could help create metal-like substances for jewelry and electronics.

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