Nanfang Yu, assistant professor of applied¹ physics at Columbia Engineering, and colleagues from the University of Zürich and the University of Washington, have discovered two key strategies that enable Saharan silver ants to stay cool in one of the hottest terrestrial environments on Earth. Yu's team is the first to demonstrate that the ants use a coat of uniquely shaped hairs to control electromagnetic waves over an extremely broad range from the solar spectrum² (visible and near-infrared³) to the thermal⁴ radiation spectrum (mid-infrared), and that different physical mechanisms⁵ are used in different spectral⁶ bands to realize the same biological function of reducing body temperature. Their research, "Saharan silver ants keep cool by combining enhanced optical reflection and radiative heat dissipation," is published June 18 in Science magazine. "This is a telling example of how evolution has triggered the adaptation of physical attributes to accomplish a physiological⁷ task and ensure survival, in this case to prevent Sahara silver ants from getting overheated," Yu says. "While there have been many studies of the physical optics of living systems in the ultraviolet and visible range of the spectrum, our understanding of the role of infrared light in their lives is much less advanced. Our study shows that light invisible to the human eye does not necessarily mean that it does not play a crucial role for living organisms."

 

The project was initially⁸ triggered by wondering whether the ants' conspicuous⁹ silvery coat was important in keeping them cool in blistering¹⁰ heat. Yu's team found that the answer to this question was much broader once they realized the important role of infrared light. Their discovery that that there is a biological solution to a thermoregulatory problem could lead to the development of novel flat optical components¹¹ that exhibit optimal¹² cooling properties. 

 

"Such biologically inspired cooling surfaces will have high reflectivity in the solar spectrum and high radiative efficiency in the thermal radiation spectrum," Yu explains. "So this may generate useful applications such as a cooling surface for vehicles, buildings, instruments, and even clothing."

 

Saharan silver ants (Cataglyphis bombycina) forage¹³ in the Saharan Desert in the full midday sun when surface temperatures reach up to 70°C (158°F), and they must keep their body temperature below their critical thermal maximum of 53.6°C (128.48°F) most of the time. In their wide-ranging foraging¹⁴ journeys, the ants search for corpses¹⁵ of insects and other arthropods that have succumbed¹⁶ to the thermally¹⁷ harsh desert conditions, which they are able to endure more successfully. Being most active during the hottest moment of the day also allows these ants to avoid predatory desert lizards¹⁸. Researchers have long wondered how these tiny insects (about 10 mm, or 3/8" long) can survive under such thermally extreme and stressful conditions.

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