Bright, shiny spots dotting the Sahara Desert may look like particularly reflective grains of sand, but they are actually ants that have adapted to harsh desert temperatures by growing special reflective hairs on their backs.
According to a new PLOS ONE study, the body hairs of the Saharan silver ant cause total internal reflection – the reflection of light between two things – to make the insects almost ten times more reflective. This covering prevents overheating and yields a silver sheen.
The Saharan silver ant is one of the most temperature-resistant organisms on Earth. It can forage in the desert even when temperatures soar above 100 degrees Fahrenheit.
In 2015, scientists discovered that tiny body hairs allow Saharan silver ants to survive extreme heat; however, the details of the hairs’ optical properties remained unexplained.
“The ability to reflect solar radiation by means of total internal reflection is a novel adaptive mechanism in desert animals, which gives an efficient thermal protection against the intense solar radiation,” said Serge Aron, one of the authors of the new study.
Aron and colleagues used a Scanning Electron Microscope (SEM) to examine the ant hairs and trace the path of incoming light rays. They also compared normal ‘hairy’ ants with ants that had been shaved, measuring how their bodies reflected light and how quickly they heated under simulated sunlight.
The researchers found that hairy ants were almost ten times more reflective than shaved ants and were able to stay up to 35.6 degrees Fahrenheit cooler under simulated sunlight. They also confirmed that the triangular cross section and corrugated surface of each hair act like a prism to reflect light; the light rays entering each hair undergo total internal reflection, bouncing off the bottom plane of the hair instead of transmitting through it. This mirror effect gives the ant its bright silver sheen and reduces heat absorption from sunlight, preventing the ant from overheating.
“To the best of our knowledge, this is also the first time that total internal reflection is shown to determine the color of an organism,” Aron said.
Most arthropods have cylindrical or plate-like body bristles, so these results may be specific to this ant species. Nonetheless, the authors state that the new findings improve understanding of the Saharan silver ant’s unusual color and ability to survive in the desert heat.
Research Article: Willot Q, Simonis P, Vigneron J-P, Aron S (2016) Total Internal Reflection Accounts for the Bright Color of the Saharan Silver Ant. PLoS ONE 11(4): e0152325. doi:10.1371/journal.pone.0152325
Image Credit: Frame A from Fig 1. of the manuscript.