Study explains how jewel scarab beetles appear golden

"We have learned that there is great subtlety and detail to be found in these optical signatures," said researcher Ewan Finlayson.
By Brooks Hays   |   June 16, 2017 at 10:33 AM

June 16 (UPI) -- The jewel scarab beetles of Central America appear as if they've been carved from pure gold. New research explains how.

Scientists at the University of Exeter in Great Britain conducted experiments that suggest the beetle's unique "optical signature" is created by the color, texture and structure of its exoskeleton.

The beetle's uniquely textured exoskeleton alters the polarization of the light reflected off its black body. Polarization describes the orientation of a light wave's oscillation or spin.

The golden scarab beetle's optical signature is "optically-ambidextrous," which means its exoskeleton reflects both left-handed and right-handed polarized light.

"This characteristic of Chrysina resplendens appears to be an exceptional and wonderfully specialised characteristic in currently known animals and plants," Pete Vukusic, a physicist at Exeter, said in a news release. "It will serve as a valuable platform from which bio-inspired optical technologies can spring."

Researchers published their analysis in the Journal of The Royal Society Interface.

Other scarab beetle species, such as those prized and worshipped by ancient Egyptians, appear to be colored in brilliant metallic blues and greens. But most don't reflect polarized light. The golden scarab beetle is unique.

"We have learned that there is great subtlety and detail to be found in these optical signatures and in the elaborate natural structures that generate them," research fellow Ewan Finlayson said.

A combination of chitin and other proteins create the jewel scarab's exoskeleton and its microstructures. Researchers aren't exactly sure why the beetle adopted an exoskeleton with such unusual optical characteristics.

It's possible the golden hue helps the beetle blend in to its surroundings. When the beetle moves, the golden sheen may disorient would-be predators.

"There are many species which are iridescent but jewel beetles are one of the most charismatic and brightly colored, and their color might be used in mating," said Martin Stevens, professor of evolutionary ecology at Exeter. "However, it is not clear how other beetles see the gold color and reflected light. Many small mammals would not be able to distinguish the golden color from reds, greens, and yellows, but a predatory bird would likely be able to see these colours well."

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