Science & Environment

Beetles' whiteness understood

Beetle Image copyright University of Cambridge
Image caption The scales of these beetles are the whitest, lightest known

Scientists say the secret behind the super-whiteness of some beetles lies in the complex molecular geometry of their scales, which are able to scatter light with supreme efficiency in spite of their thinness.

Cyphochilus beetles are whiter than paper or any artificial material produced so far. But researchers are only now starting to fully explain the beetles' trick.

Understanding the physical mechanisms could allow manufacturers to produce whiter paper, plastics and paints.

Dr Silvia Vignolini, of the University of Cambridge and co-author of a research paper published in Scientific Reports, told BBC News: "We were inspired by the work of Prof Pete Vukusic, because when we saw these beetles that were so white we were quite puzzled."

Prof Vukusic had been studying the impressive light properties of the beetles for a number of years.

At that time, Dr Vignolini consulted lead author Dr Matteo Burresi, from the European Laboratory for Non-linear Spectroscopy in Florence, Italy.

"[We thought] we should try to do a proper study on the light propagation in these beetles to understand the main characteristics of the network that provide such brightness," Dr Vignolini said.

Image copyright Cambridge University
Image caption The scientists found a complex and dense network of elongated filaments inside the scales

White is the combination of all the colours that we can see.

Therefore, to produce white scales, Cyphochilus beetles must deflect all colours with equal strength, something rarely found in nature.

Intense colours are usually obtained by adding as many layers of a material as possible.

Dr Vignolini used as an example a red wall that we want to paint white.

As we add coats of white, we see less of the red underneath it, making the paint thicker, less transparent, and whiter.

But the incredible thing about Cyphochilus beetles is that their scales are extremely white and extremely thin at the same time.

What makes these scales so white is the special arrangement of the chitin elements inside them, together with their varied shapes and sizes.

Image copyright Cambridge University
Image caption The beetles have developed white shells to be camouflaged among white fungi

The chitin filaments are just a few millionths of a metre thick - far thinner than a very fine sheet of paper.

The elements are tightly packed, scattering light efficiently, but still able keep a degree of disorder in their shape.

Dr Vignolini explained that, "these elements are elongated, but some of them are shorter, some of them are bigger".

Disorder is important to keep the beetle white.

To create other colours, "you need to have [the elements] ordered".

Cyphochilus beetles are native to South-East Asia, where they live among white fungi.

This new study proves that they have been optimised by natural selection to be camouflaged among their surroundings, while keeping the scales as light as possible - which is crucial for flying insects.

Dr Burresi's team says there are other beetles that are as bright as Cyphochilus, but to achieve this, the animals have had to nearly double the thickness of their scales.

"What is difficult is to make this high-scattering effect with a thin material, and this is what the Cyphochilus is good at."

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