Scientists have identified two major strategies Saharan silver ants use to stay cool in the blazing hot environments they inhabit.
The researchers are the first to demonstrate that these ants use a "coat" of uniquely-shaped hairs to control electromagnetic waves from the solar spectrum (visible and near-infrared) to the thermal radiation spectrum (mid-infrared), Brookhaven National Laboratory reported. The team also identified the different physical mechanisms used in different thermal spectral bands that effectively 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 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." Nanfang Yu, assistant professor of applied physics at Columbia Engineering.
The discovery provides a "biological solution to a thermoregulatory problem" that could contribute to the development of flat optical devise that have incredible 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."
The incredible ants looked at in the study forage for food in the Saharan Desert during the height of the day, when temperatures can reach a scorching 158 degrees Fahrenheit. Being active at this time of day helps protect the ants from predators that cannot handle the heat.
To determine how the ants survive under such extreme temperatures, the researchers used electron microscopy and ion beam milling, and found the insects are coated with uniquely shaped hairs with triangular cross-sections. The hair keeps them cool by reflecting visible and near-infrared light, while simultaneously working as an antireflection layer that enhances the ants' ability to shed excess heat via thermal radiation, which is emitted from the body of the ant into the sky.
"To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning," says Yu. "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 researchers found these functions reduced the body temperature of the ants by five to 10 degrees compared to when they were without hair cover, demonstrating an incredible evolutionary feat. In the future, the researchers plan to perform the same research on other animals living in extreme conditions to determine the unique ways in which they survive.
"Animals have evolved diverse strategies to perceive and utilize electromagnetic waves: deep sea fish have eyes that enable them to maneuver and prey in dark waters, butterflies create colors from nanostructures in their wings, honey bees can see and respond to ultraviolet signals, and fireflies use flash communication systems," Yu said. "Organs evolved for perceiving or controlling electromagnetic waves often surpass analogous man-made devices in both sophistication and efficiency. Understanding and harnessing natural design concepts deepens our knowledge of complex biological systems and inspires ideas for creating novel technologies."
The findings were published in a recent edition of the journal Science.
