Transfiguration butterflies can achieve an almost invisible effect. Image source: AARON POMERANTZ
In the Panamanian rainforest, Aaron Pomerantz, an integrative biologist at the University of California, Berkeley, set up a small tent. It was his makeshift field laboratory, equipped with microscopes, chemical reagents and other laboratory equipment.
Sometimes, in hot weather, Pomerantz struggles to avoid sweat contaminating vulnerable Lepidoptera specimens. He was looking for a transparent butterfly with "invisible wings", the broad-striped black-veined butterfly (commonly known as the transfiguration butterfly).
This rare butterfly is "like a ghost in the rainforest". Now, Pomerantz and his phD supervisor, Nipam Patel, have not only found the transfiguration butterfly, but also solved the mystery of how the wings of the transfiguration butterfly become transparent.
The rare feature of transparent wings helps the transient butterfly avoid predators. Compared to other species with transparent wings, such as dragonflies, transient butterflies are better at flying in rainforests without being noticed because their wings neither glow nor flicker in the sun.
The wings of a butterfly consist of a thin layer of chitopolysan, a natural polymer of membranes, usually covered with tiny scales that resemble tiles.
The team found that not only did the transfiguration butterfly wings have fewer scales, but many of them were also converted into bristles, making it easier for light to pass through the wings. Through electron microscopy scanning, Pomerantz also found that the mounds between these bristles, known as nanolevels, were covered by a layer of wax.
Pomerantz said the nanostallations appear to help reduce glare. This glare is usually produced when light hits the surface of an object and is reflected out at the same angle, just as light is reflected on a mirror. These nanospoles make the surface of the wings "rough" and can reflect light from multiple angles, thereby breaking down the strong light reflection. The study was recently published in the Journal of Experimental Biology.
In addition, the wax coating slows down the speed of light passing through the wings. This decrease in speed weakens the effect of light on the scales on the wings, further reducing reflected light. Pomerantz says the wings become sparkling when stripped of the wax coating and nanotubes.
Experts believe the results could help researchers effectively channel light into solar panels and make cheaper anti-reflective lenses for cameras or glasses. But for now, Pomerantz and Patel hope to focus first on how transfiguration butterflies evolved from their opaque wing ancestors and use genomics to identify key genes. (Xu Rui)
Source: China Science Daily