Why would anyone want to take the temperature of a butterfly? Thermal imaging the wings of these small creatures could help researchers understand how insects adapt and survive extremely high temperatures. Such work not only contributes to a better understanding of insect thermoregulation, but it also may inspire technological advancement in nanotechnology as well as in aircraft.
“We wanted to find out how small animals were hardwired to survive extreme heat,” said Nanfang Yu, associate professor of applied physics at Columbia, in a recent press release. “The interesting thing here is understanding how small and light insects—tiny ants or the thin wings of butterflies—manage thermodynamically, because they are, by default, very bad at it,” Yu explained. Given their small thermal capacity, small animals like insects can heat up to extreme temperatures within a few seconds, he noted.
Yu has studied insect temperature before, and his latest study, conducted by researchers from Columbia Engineering and Harvard University, continues the quest into understanding how small insects manage to keep cool. Using thermal imaging, the team identified the features in butterfly wings that aid in thermoregulation. With a thermal camera such as Teledyne’s FLIR T865, “you begin to essentially see the skeleton of the butterfly,” said Yu. “It’s almost like an x-ray—you are seeing the framework, the wing veins, the membrane… the whole cross section of the wing material.” During thermal imaging, the bright colors and patterns of a butterfly wing all disappear, and what is seen instead is the underlying structure of the wing itself, Yu added.
That wing structure includes mechanical sensors for detecting overheating as well as scales that contain nanostructures for radiative cooling. Yu’s team was also able to measure the difference in temperature between the wing veins, membrane, and other elements. They found that the areas of butterfly wings that contain live cells (wing veins) have higher thermal emissivity than the “lifeless” regions of the wing (the membrane).
Yu believes such findings could inspire designs of heat-resistant nanostructures as well as heat-sensing aircraft.
Thermal imaging was found to be the most noninvasive way to measure temperature, according Yu. “This imaging technique enables us to examine physical adaptations that decouple the wing’s visible appearance from its thermodynamic properties,” Yu said in an article from Columbia Engineering. “We discovered that diverse scale nanostructures and nonuniform cuticle thicknesses create a heterogeneous distribution of radiative cooling—heat dissipation through thermal radiation—that selectively reduces the temperature of living structures such as wing veins and scent pads.”
Some challenges do occur with thermal imaging because the butterfly wing is semi-transparent in infrared, so “when you are looking at a butterfly wing in a thermal camera, you’re not just receiving the thermal radiation of the wing itself, you’re also receiving the thermal radiation generated by the background behind the wing." To get a true temperature reading of a butterfly wing, Yu’s team had to quantify the emissivity and reflectivity of the wing and remove those sources of background temperature from their measurements, it was reported.
Yu and his colleague Naomi E. Pierce, Hessel Professor of Biology, plan to continue their research on butterfly wings. Pierce is the curator of Lepidoptera at the Museum of Comparative Zoology at Harvard. They are currently conducting an extensive scan of the collection using a thermal camera and aim to identify the factors that contribute to the design of a butterfly wing. Yu compares the work to “deciphering a complex book” because of the many diverse elements that have played a part in the evolution of the butterfly wing.