From even a short distance, this West African Gaboon viper looks just like a pile of dead leaves. New research shows that the highly-camouflaged snake owes its elusiveness to nanostructures in its black scales.
The velvety-black patches on this snake's back are so dark and absorb so much light, they look like gaps in the snake’s body. This illusion allows the lurkers to dissolve into leaf litter as they wait for prey on the rainforest floor.
To determine what makes these scales appear so black, a team of German scientists examined the snake’s skin under a scanning electron microscope (SEM), and found differences in the nanostructures of dark and pale scales that explain the high contrast, the team reports today in Scientific Reports.
SEM images showed that surface textures are more pronounced in black scales than in pale scales. Black scales have densely-packed, jagged microstructures, whereas lighter scales have much duller, sparser bumps. At higher resolutions, intricate maze-like “nanoridges” appear etched within microstructures on both scales, but are more elaborate in the black ones.
To test whether these distinct structures -- and not pigments -- account for the darkness, the team coated tan and dark scales in a thin layer of gold-palladium. They found that tan scales took on the metallic luster of the gold coating, but the black ones remained black even with their pigments masked. This confirmed that structure takes precedence over pigment.
Such light-absorbing “microornaments” have never been identified in snakes before, though similar structures are well documented in butterfly wings.
Still, the team does not quite understand what causes these particular structures to absorb so much light. They believe the intricate textures could help guide sunlight deep into the scale where a dark pigment absorbs it, but this remains uncertain.
“We have just explained the effect and its main features,” Alexander Kovalev, a co-author on the paper from Kiel University, told Wired. “But it is still not clear how the nanostructures work, or where this ultra-black coloration comes from.”
The team plans to continue studying these scales to better understand the optics of the camouflage. Ultimately, their findings could help engineers design ultra-black artificial materials, useful in a variety of capacities from military camouflage to solar heat collectors.
