Harvard, Columbia Scientists Elucidate Cooling Mechanisms in Butterfly Wings

Scientists at Harvard and Columbia released a study examining the structures and cooling mechanisms of butterfly wings, with possible implications for construction and aeronautical engineering.

The paper, published at the end of last month, reported the presence of a “wing heart” that pumps hemolymph — a circulating fluid equivalent to blood in insects — through butterfly wings, providing evidence that these wings are living, dynamic systems.

Naomi E. Pierce, a Harvard professor of biology and co-author of the paper, said that while previous research had identified wing hearts in the thorax of insects, the study found them in a formerly undescribed location.

“This wing heart was right smack in the middle of the wing,” Pierce said.

Nanfang Yu, a professor of applied physics at Columbia University and co-author of the study, wrote in an email that the research team hypothesizes butterflies have cooling mechanisms to protect their wings.

“Butterfly wings have intrinsically poor thermodynamic properties: given their small thermal capacity, wings can overheat rapidly in the sun to physiologically disastrous high temperatures,” Yu wrote. “Our thermodynamic experiments show that the wings of living butterflies in the sun can reach a peak temperature as high as 60 degrees Celsius within 10 seconds.”

Yu added that butterflies had adapted to reduce solar absorption in near-infrared light and emit more heat at dynamic parts of the wing. Alongside these physical mechanisms, the study also described several behavioral adaptations of butterflies that help keep their wings cool.

“In an experiment, we locally heated up the living regions of the wings of living butterflies using a small laser spot,” Yu wrote. “All species tested responded with specialized behaviors to prevent overheating of their wings. Some flap their wings, some turn around, and others walk away from the laser spot.”

Cheng-Chia Tsai, a graduate student at Columbia and lead author of the study, said these cooling processes are crucial to butterflies, as overheating the wings impeded their capabilities.

“The butterfly wing started to become insensitive,” Tsai said. “They don’t feel the temperature anymore. So this means overheating will damage the sensors, which includes the mechanical sensors.”

Pierce said the findings from the study are already being applied towards the making of a new type of paint that is similar to butterfly wing nanostructures and forms “little bubbles” as it dries. When used in a building, the paint cut down costs of air-conditioning by 30 percent, according to Pierce.

Yu wrote that the results of the study can also provide insights for airplane wing construction.

“The sensory networks discovered in the wings certainly provide us a lesson that the design of the wings of flying machines should not be solely based on considerations of aerodynamics,” Yu wrote. “Maybe we can create bioinspired, robust, and multifunctional sensory networks for airplane wings that can detect the external environment and the internal state of the wing, and provide a real-time fail-safe against failure of individual elements in the network.”

—Staff writer Ethan Lee can be reached at ethan.lee@thecrimson.com.