An invisible butterfly might sound like something from a fairytale, but there are butterflies with wings as transparent as panes of glass.
The reason that their wings are transparent is because they barely reflect any light. A wide spectrum of light—from infrared to visible to ultraviolet—travels straight through the wing tissue.
You might be wondering why any butterfly would want to be invisible. Well, it turns out that the life of an insect that is prey to birds, toads and rats is greatly improved by being difficult to see. Birds, in particular, struggle to track a glasswing butterfly while it is in flight.
The property of the wing tissue that produces the butterfly’s transparency seems to go against nature’s instinct. The nanostructures on the surface of the butterfly’s wings are completely random, researchers report in Nature Communications. They seem to be scattered onto the wing surface with no regard for regular size or structured distribution. This means that when rays of light strike the surface of the wing, one or two rays are reflected, but the majority of the light can pass straight through the wing, unhindered by the surface.
Irregularity of the size and distribution of nanostructures on the surface of the butterfly wing causes low reflection of light at all view angles. (Photo: Radwanul Hasan Siddique, KIT)
Doctoral student Radwanul Hasan Siddique, who discovered this effect, commented on the unsystematic nature of the butterfly’s wings: “In contrast to other natural phenomena, where regularity is of top priority, the glasswing butterfly uses an apparent chaos to reach effects that are also fascinating for us humans.”
You might be surprised to know that these butterflies are leading the way towards water-repellent technology. Using the random nanostructure surface of the glasswing butterfly for inspiration, we can create coatings for digital screens that can be seen in the glaring sunlight. The first prototypes of this technology have also indicated that this type of surface coating is water-repellent and self-cleaning! Good news for clumsy phone users everywhere!