How do Saharan Silver Ants remain cool in one of the warmest climates on the planet? A group of research engineers has found the answer to that question, adding that its findings could lead to the development of flat optical components with excellent cooling properties.
The multinational project was a joint collaboration between Columbia University, the University of Zürich and the University of Washington. The team discovered the ants rely on a coat featuring unique hair that helps them control a broad range of electromagnetic waves, including visible and near-infrared. Different spectral bands call for different physical mechanisms to reduce body temperature.
“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 Saharan silver ants from getting overheated,” says Nafgang Yu, an assistant applied physics professor at Columbia Engineering. “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.”
Yu and his team initially set out to discover what role the ant’s coat plays in helping it cool down. Once they concluded that infrared light plays an important role, they broadened their net. Their discovery could help improve optical components for cooling purposes.
“Such biologically inspired cooling surfaces will have high reflectivity in the solar spectrum and high radiative efficiency in the thermal radiation spectrum,” Yu adds. “So this may generate useful applications such as a cooling surface for vehicles, buildings, instruments, and even clothing.”
Saharan silver ants are active in the midday sun, when temperatures can reach scorching highs of 158°F. To survive, the ants need to assure their body temperature stays below their critical thermal maximum of approximately 128.5°F. Foraging during the warmest period of the day offers a number of advantages to the ants, including avoiding predators such as desert lizards.
But how exactly do these tiny creatures cool their body temperature? Yu and his team used electron microscopy and realized that the ants’ bodies are coated with hairs containing triangular cross-sections. These hairs are responsible for cooling the animals in two ways. Firstly, they’re highly reflective under both visible and near-infrared light (the maximum solar radiation region). The hairs also happen to be highly emissive in the electromagnetic spectrum’s mid-infrared region. They act as an antireflection layer that helps the ant offload excess heat by way of thermal radiation. According to the researchers, the “passive cooling effect works under the full sun whenever the insects are exposed to the clear sky.”
“To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning,” Yu adds. “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.”
The engineers say these natural cooling techniques help reduce the ant’s body temperature by up to 10 degrees. “The fact that these silver ants can manipulate electromagnetic waves over such a broad range of spectrum shows us just how complex the function of these seemingly simple biological organs of an insect can be,” said Nan Shi, a PhD student who works alongside Yu.
The group plans to expand its research and look into other animal species and how they manage extreme weather. A research paper, titled “Saharan silver ants keep cool by combining enhanced optical reflection and radiative heat dissipation,” was recently published in Science magazine. For more information, visit Columbia University’s website.