International. Butterfly wings are very sensitive to heat. Excessive exposure to sunlight could cause their wings to overheat, while too low temperatures could freeze them. A team of engineers and biologists from Columbia Engineering, Harvard University and the University of Washington has identified a network of mechanical and temperature sensors inside butterfly wings.
A butterfly wing absorbs sunlight and exchanges energy through thermal radiation with the environment, including the terrestrial environment below the wing and the sky above. The radiative energy emitted from the hot wing into the cold sky represents an important heat dissipation channel in addition to heat losses by convection.
The research team examined the butterflies' wings under wavelengths of light ranging from ultraviolet to visible to mid-infrared. In the visible, the colored parts of the wings are associated with the absorption and reflection of sunlight. Meanwhile, in the near-infrared, butterfly wings have a lower solar absorption capacity. Since sunlight is about 50% less powerful in the near-infrared, lower absorption of the near-infrared helps reduce the overall temperature of the wings.
In addition, different parts of the butterfly wing have different thermal emissivity. Parts containing living cells have high thermal emissivity close to the unit; which is perfect for heat dissipation by thermal radiation. Hyperspectral imaging has shown that the average temperature of parts containing living cells is always lower than that of parts of "lifeless" wings. For the "living part" of the wing, the high thermal emissivity is caused by flakes with unique nanostructures along with thick layers of membrane.
In addition to these structural aspects, butterflies can also react to the intensity and direction of sunlight. They move in ways that allow them to displace the thermal stimuli applied to their wings. Simulated environmental conditions using laser beams have shown that these reactions occurred whenever a laser spot was directed at the "living" components on the wings; suggesting that they may contain a network of thermal sensors.
This research could lead to several applications for temperature distribution in objects that are light and translucent such as butterfly wings. The nanostructures found in the wing flakes could inspire the design of radiative cooling materials to help control excessive heat conditions.
