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Secret of why jewel scarab beetles look like pure gold

The ornate beetles or Jewel Scarab Beetles have a brilliant metallic gold color and are highly valued by collectors. But until now the reasons behind their golden iridescent hue, have not been fully understood.

University of Exeter physicists specializing in color and light have done trials exploring the origin of the scarab beetles’ striking metallic golden appearance, showing that the golden beetles have a unique’ optic hand’. The structure of the beetle and its armor manipulates the way the light is reflected so that it looks like pure gold.

Golden Scarab Beetle (Plusiotis resplendens) portrait on leaf, Monteverde Cloud Forest Reserve, Costa Rica
Golden Scarab Beetle (Plusiotis resplendens) portrait on leaf, Monteverde Cloud Forest Reserve, Costa Rica

Professor Pete Vukusic found that the golden appearance is due to the high reflectiveness of the beetles’ exoskeleton, which also manipulates a property of the light called its polarization: the orientation of the reflected light wave’s oscillations.

Professor Vukusic said: “The golden color and distinctive polarized reflection from the Scarab beetle sets him fully apart from many different stunning and bright colored animals and plants. His body incorporates a bright and golden look that reflects each right-handed and left-handed circularly-polarized lightweight at the same time. This characteristic seems to be Associate in Nursing exceptional and splendidly specialized characteristic in presently acknowledged animals and plants.

Egyptians used Scarab Beetles as amulets, which were used to be wrapped in the bandages of mummies, are a jewel-like green and blue colors. The majority of brightly-colored beetles tend to be green and do not reflect polarized light. In comparison to golden beetles these beetles lack more specialized aspects of their exoskeleton’s finely detailed structure.

Dr. Ewan Finlayson said: “We were drawn to the study of this jewel scarab not only by its striking metallic golden appearance, but also by its ability to control a less obvious property of the reflected light: the polarization. There is great subtlety and detail to be found in these optical ‘signatures’ and in the elaborate natural structures that generate them.”

These golden jewel scarab beetle ( Chrysina resplendens ) are mainly found in the Americas, has evolved an exoskeleton that contains intricate nano-structures which is responsible for its appearance.

The nano-structured exoskeleton is made-up of natural materials including chitin and various proteins. These structures are remarkable in the way they manipulate the way polarized light is reflected.

The experiments made on the work of an early American scientist called Michelson, looked at the polarized reflection from many different beetles, and on the work of Anthony Neville (then at Bristol University) in 1971, who began looking more closely at Chrysina resplendens.

These scarabs typically live in mountain forests. Their larvae feed on rotting logs of various tree species, while the adults Scarab Beetles feed on foliage. The larval form lasts for several months to a year, and pupation takes a month or two. After the adult emerges it lives for about a further three months.

Another explanation for the highly-reflective appearance of these beetles exoskeleton is crypsis  ( the ability of the animal to blend in to its surroundings ).

Dr Martin Stevens said: “It is not absolutely clear why these beetles are a bright golden color, but one option is that it somehow works in camouflage. The shiny golden color could also change how the beetle is seen as it moves, potentially dazzling a would-be predator. 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 would likely be able to see these colors well.”

Article Source: Materials provided by University of Exeter. Note: Content may be edited for style and length.

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