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Viper's velvet black spots key to camouflage

Master of disguise Scientists have identified nanostructures in the ultra-black skin markings of an African viper that could inspire the quest to create the ultimate light-absorbing material.

The West African Gaboon viper (Bitis rhinoceros), one of the largest in Africa and a master of camouflage, has dark spots in the geometrical pattern of its skin that are deep, velvety black and reflect very little light.

Interwoven with white- and brown-coloured scales that are very reflective, this creates a high contrast that renders the snake difficult to spot on the richly-patterned rainforest floor.

The team of German scientists from Kiel University and the University of Bonn set out to find the secret behind the black spots' ultra-darkness.

To do this they compared the topography of the velvet black and pale scales.

They discovered the scale surface of the black areas was made up of tightly-packed, leaf-like microstructures covered in turn with nanometre-sized ridges.

One nanometre is equivalent to a billionth of a metre.

"The microornamentation in velvet black regions of the Gaboon viper skin is unique among snakes," they report in the journal Scientific Reports .

"Leaf-like microstructures with both nanoridges and hair-like nanoprotuberances that coincide with black skin colouration have never been described before."

Master of camouflage

The team theorise that the micro- and nanostructures, which protrude at slightly different angles, scatter and trap incoming light.

The pale scales reflected and transmitted more light than the dark scales. Differences in reflectance between pale and black scales were higher at short wavelengths of light below 600 nanometres -- a wavelength that corresponds with blueish-green colours.

This pattern of colouration provides the perfect camouflage ambushing prey in the low light at dawn and evening, or the green light in forests or blue light in clearings during the day.

The researchers say the low reflecting properties of the velvet black spots also have implications for enhancing the darkness of artificial materials.

"The structure-based velvet black effect could also be potentially transferred to other materials," they write.

The search for a high-absorbing, low-reflecting artificial material is highly prized in science for its potential use in specialised optical systems or solar heat capture, for example.

Some artificial ultra-black surfaces are already darker than the snake's spots, says study lead author Marlene Spinner of the University of Bonn's Institute of Zoology.

But introducing the snake's nanotechnology could potentially enhance their light absorbancy even more.

"The micro-ornamentation on the snake's velvet black scales is a further example that the same physical law applies to both nature and technology and leads consequently to similar constructions," say the researchers.