In a world filled with technology, some of the most sophisticated designs exist in nature. Butterfly wing anatomy, for example, is delicate, complicated and efficient. Butterfly wings are also extremely fragile and sensitive to temperature changes, so what prevents them from overheating?
How to Study Butterfly Anatomy
Researchers at Columbia University and Harvard University used a new technique called infrared hyperspectral imaging to find out how butterfly wings avoid overheating. They learned that butterfly wings are based on a complex thermodynamic structure that can teach us about how to make more efficient cooling materials.
The researchers anesthetized butterflies and then used a paintbrush to carefully remove the wing scales to reveal the wings’ nanostructure. They also injected a blue stain into the butterfly’s thorax. This stain was then carried by hemolymph, which is like a bug’s version of blood, so it spread throughout the butterfly’s living cells and tissues, making it easier for the scientists to see the tiny details and go deeper than butterfly wing anatomy.
However, even with a stain, it is difficult to study how butterfly wings manage heat. According to ScienceNews, butterfly wings are so thin and semi-transparent that thermal cameras can’t distinguish the difference between heat from the wings or other things in the background. To get around this challenge, the Columbia-Harvard team designed a technique based on infrared hyperspectral imaging where each pixel of an image represents an infrared spectrum. Then they used this special thermal camera to map the way heat dissipated from certain areas on the delicate wings of more than 50 butterfly species.
What Keeps Butterfly Wings From Overheating?
With this new imaging technique, the researchers were able to map out the thermodynamic properties that make butterfly wings so efficient, as well as gain a deeper understanding of how the insect’s body works as a whole.
“This work shows that we should reconceptualize the butterfly wing as a dynamic, living structure rather than as a relatively inert membrane,” said Naomi E. Pierce, a biology professor at Harvard who co-led the new thermodynamic research. “Patterns observed on the wing may also be shaped in important ways by the need to modulate temperatures of living parts of the wing.”
They discovered a “wing heart” that beats a few dozen times per minute to control blood flow to the scent pads of certain species of butterflies. More surprising, they discovered that butterfly wings contain a network of mechanical and temperature sensors that work similarly to a household radiator heater.
Butterfly wings contain a mixture of living and nonliving structures covered by scales made of a rigid substance called chitlin, according to Scientific American. The live portions of wings have scent pads, pheromone-releasing organs and veins; chitlin membranes stretch between the wing veins.
It turns out that the scales covering different parts of the wing have different shapes to help regulate the wing’s heat. Butterfly wings don’t overheat because of a process called radiative cooling, according to Scientific American. Because heat is electromagnetic radiation generated by the vibration of molecules, when a material exposes more molecules on its surface it will be able to dissipate more heat. Therefore, the structure of materials will allow them to release heat more quickly than others.
There is one type of scale that covers the wing’s non-living parts, which aren’t as sensitive to heat. Then there are special scales to cover the living parts of the wing that are more susceptible to overheating. Scales over the scent pads are shaped like a bunch of tiny tubes, similar to radiators but only one micron in diameter. Just like a household heater, these nanostructures are shaped to efficiently dissipate warmth. While the radiator-style scales help protect the wing’s organs from overheating, the scales covering veins are also efficient at emitting heat, although they are thicker, with many holes.
The Columbia and Harvard researchers also experimented with how butterfly wings handle different environmental conditions. They varied the light and temperature and found that this radiative cooling anatomy caused the live areas of butterfly wings (the veins and scent pads) to always be cooler than the lifeless areas of the wings.
Butterfly wings are joining a growing list of nature that inspires technology. Because of their complex thermodynamic structures, butterfly wings can teach us how to make more efficient cooling materials. The researchers are using what they learned from butterfly wings, along with other studies they’ve done on sub-Saharan ants, to develop a cooling polymer and spin it into nanostructures inspired by butterfly wing anatomy.
This material could be used to coat structures such as buildings to help them get rid of heat. Similar heat-repellent materials are often white because that color doesn’t absorb heat. But as a bonus, just like butterflies, this new lightweight cooling material could be made in a variety of colors.
Butterfly-inspired cooling materials would be especially useful for developing heat-resistant aircraft. Nature is the ultimate inspiration for aircraft. Someday, airplane wings could be as efficient as butterfly wings.