Unique Reflective Hairs Keep Sarahan Silver Ants Cool

Posted on June 19, 2015

Sarahan Silver Ant coat

Scientists have discovered that Saharan silver ants have unique hairs that help them stay cool in the hot Saharan Desert sun. The metallic-like coat of silver hairs enables the ants to control electromagnetic waves over an extremely broad range from the solar spectrum to the thermal radiation spectrum. The scientists say the ants keep cool by combining optical reflection and radiative heat dissipation.

The discovery was made by Nanfang Yu, assistant professor of applied physics at Columbia Engineering, and colleagues from the University of Zurich and the University of Washington. Yu says in a statement, "This is a telling example of how evolution has triggered the adaptation of physical attributes to accomplish a physiological task and ensure survival, in this case to prevent Sahara silver ants from getting overheated. 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."

Temperatures in the Saharan Desert can reach 70°C (158°F) and the ants need keep their body temperatures below 53.6°C (128.48°F) most of the time. The scientists used electron microscopy and ion beam milling to study the ants' silver coats. The scientists found the hairs are highly reflective under both visible and near-infrared light. The hairs are also highly emissive in the mid-infrared portion of the electromagnetic spectrum. This serves as an anti-reflection layer that enhances the ants' ability to offload excess heat via thermal radiation.

Hu says, "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."

A research paper on the coat of the Sarahan silver ants was published here in the journal, Science.

Photo: Norman Nan Shi and Nanfang Yu, Columbia Engineering