The hair of the Saharan silver ant keeps it cool by efficiently reflecting light and heat energy while also dissipating excess heat.

Edit Hook

Saharan silver ants (Cataglyphis bombycina) have a remarkable ability to thrive in one of the hottest regions on the planet—the Sahara Desert. Unlike the sleek skin, shells and scales of most high-temperature dwellers, these ants have a unique exterior defense mechanism to beat the heat: hair.

The hair of Saharan silver ants reduces heat absorption by efficiently reflecting sunlight and dissipating heat. This enables the ant to stay cool in the midday Sahara, where temperatures can reach up to 47°C (117°F). The hairs, with their unique shape, achieve this through three distinct mechanisms:

First, 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 is achieved through the unique prism shape of the hairs, which have a flat base that lies against the body of the ant, while the other two sides are grooved (see gallery images). When light enters through one of the grooved sides, it reflects off of the base, and then exits from the other grooved side. A groove concentrates a ray of light onto a certain part of the hair in order to optimize its path of exit and thus maximize TIR. 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.

Second, the hairs also reduce heat absorption by reflecting sunlight (solar radiation) from both visible and non-visible parts of the electromagnetic spectrum, including the near-infrared (NIR). It is in these two regions that solar radiation is at its most powerful.

And third, the silver ant has 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. Ant researcher Nanfang Yu explains: “To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning. Half of the energy loss at that moment is due to thermal radiation, since your skin temperature is temporarily much higher than that of the surrounding environment.” This mechanism enables the ant to maximize the amount of heat it emits and cool itself off. The last two mechanisms cool the ant off by an additional 5-10°C, enabling the silver ant to withstand temperatures up to 53.6°C (128.48°F).

Edit Summary

References

“The [ant] hairs have a triangular cross-section with two corrugated surfaces allowing a high optical reflection in the visible and near-infrared (NIR) range of the spectrum while maximizing heat emissivity in the mid-infrared (MIR). Those two effects account for remarkable thermoregulatory properties, enabling the ant to maintain a lower thermal steady state and to cope with the high temperature of its natural habitat.”

Journal article
Total internal reflection accounts for the bright color of the Saharan silver antPLoS OneJanuary 1, 2016
Willot Q, Simonis P, Vigneron JP, Aron S

Book
Dryland Climatology.Cambridge University Press.January 1, 2011
Nicholson, SE

“[The hairs] enhance not only the reflectivity of the ant’s body surface in the visible and near-infrared range of the spectrum, where solar radiation culminates, but also the emissivity of the ant in the mid-infrared. The latter effect enables the animals to efficiently dissipate heat back to the surroundings via blackbody radiation under full daylight conditions.”

Journal article
Keeping cool: Enhanced optical reflection and heat dissipation in silver ants.ScienceJanuary 1, 2015
Nan Shi N, Tsai C, Camino F, Bernard, GD, Yu N, Wehner R.

Journal article
Passive radiative cooling below ambient air temperature under direct sunlight.NatureJanuary 1, 2014
Raman AP, Anoma MA, Zhu, L, Rephaeli E, Fan, S

“To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning. Half of the energy loss at that moment is due to thermal radiation, since your skin temperature is temporarily much higher than that of the surrounding environment.”

Web page
Staying cool: Saharan silver antsColumbia EngineeringJanuary 1, 2015
The Fu Foundation School of Engineering and Applied Science

Edit References

Living System/s

Organism
Saharan Silver AntCataglyphis bombycinaspecies

Edit Living Systems