Butterfly wings are scale-covered complex tissues which do much more than keep these insects aloft.
Butterfly wings may attract mates, warn potential predators to stay away, mimic other animals, or provide camouflage. All these roles depend upon wing coloration, which is unchanging. The scales which color a butterfly’s wings do so using pigments and nanoscale microstructures which are elaborately layered to produce iridescence.
Insects are ectothermic: unable to internally regulate their thermal status. They compensate by sunning themselves, contacting warm surfaces, and exercise. Many flying insects, including bees, violently vibrate their flight muscles to raise their internal temperature.
The evolutionary thermal posture of ectothermy is much more efficient than endotherms, which can keep themselves warm to a considerable degree. Birds and mammals are endothermic. The cost of endothermy is needing to eat a lot more food.
Butterflies are diurnal. Sunburnt wings are insufferable.
Butterfly wings are thin protein membranes – a matrix of living cells which need to be keep within a small temperature range. “Given their small thermal capacity, wings can overheat rapidly in the sun,” notes Chinese American physicist Nanfang Yu.
The exquisitely designed scales and non-uniform cuticle thicknesses provide radiative cooling that keep the wing veins and androconia cool: 10–15 °C cooler than the lifeless wing parts. The androconia are the organs on butterfly wings which emit scents (pheromones) and act as the pumping heart for the wing circulatory system.
Nanfang Yu: “The insect wing is a dynamic, living structure. Butterflies use wings to sense visible and infrared radiation, responding with specialized behaviors to prevent overheating their wings.”
References:
Old World swallowtail butterfly photo courtesy of iSpfoto.
Cheng-Chia Tsai et al, “Physical and behavioral adaptations to prevent overheating of the living wings of butterflies,” Nature Communications (28 January 2020).
“There is more to a butterfly’s wing than meets the eye,” The Economist (30 January 2020).
Jason P.W. Hall & Donald J. Harvey, “A survey of androconical organs in the Riodinidae (Lepidoptera),” Zoological Journal of the Linnean Society 136: 171-197 (2002).