Saharan silver ant (Cataglyphis bombycina) keeps cool by reflecting light and dissipating heat with its triangular-sectioned silvery hair.
Saharan silver ant lives in Sahara Desert - one of the hottest places on earth - where temperatures easily reach 80°C. It has adapted itself to this extreme climate by evolving its hair into a silvery, shiny light reflecting nano-structured surface to dissipate excess heat from its body. The unique morphology of its prism-like shaped hair has a flat base that lies against the body of the ant, while the other two sides are grooved. When light enters through one of the grooved sides, it reflects off of the base, and then exits from the other grooved side. Multiple grooves enable multiple rays of light to be reflected within the same hair simultaneously. The hairs are densely packed to ensure that a minimal amount of sunlight reaches the ant’s body underneath, keeping it 2°C cooler than it would be without the hairs.
The specific shape of the hairs reduce heat absorption by maximizing the amount of light that is reflected off their surface, a process known as total internal reflection (TIR). This helps the ant cool down by 2°C. Other two benefits of the hairs cool the ant off by an additional 5-10°C. The first one is reducing heat absorption by reflecting solar radiation from both visible and non-visible parts of the electromagnetic spectrum, including the near-infrared (NIR). The second one is a particularly effective method of offloading excess heat. The shape of the hairs increases the ant’s ability to radiate heat—known as emissivity—in a specific range of the electromagnetic spectrum, the mid-infrared (MIR). Within this range, the ant’s warm body can most effectively give off excess heat energy to cooler surrounding air via thermal radiation.
Shi et al. (2015). Keeping cool: Enhanced optical reflection and radiative heat dissipation in Saharan silver ants. Science, 349. pp. 298-301.
Raman et al. (2014). Passive radiative cooling below ambient air temperature under direct sunlight. Nature, 515. pp. 540-544.