Wasps are winged insects and belong to the order Hymenoptera, which also includes ants and bees. Some wasps are black or dark blue while others have conspicuous red, orange or even yellow markings. The wings can be opaque or transparent.

The wasp in the new study, Megascolia procer javanensis, is a large robust stinging insect. It is about 5 cm long and has black opaque wings with iridescent green to bluish green reflections (figure 1). The wings are made up of chitin and melanin and are covered with a thin layer of wax. "This composite can be considered as one of the simplest optical devices," Sarrazin told nanotechweb.org.

Sarrazin and co-workers imaged the wasp's wings using reflection spectroscopy and scanning electron microscopy. The first technique allowed them to observe the different colours that were reflected from the wings and the second helped elucidate their exact nanostructure. A numerical model that computed how light propagates through the wing was also used and compared to the experimental results (figure 2 & 3).

"An important conclusion is that a very simple structure can give rise to a complex visual effect," said Sarrazin.

"Our results can be used to inspire nano and optical devices," he continued. "Depositing layers of optical material on glass is now common and this study gives an example of a similar layer on an opaque material, which could be made of steel or plastic. Indeed such layers could also produce selective reflectance in non-visible electromagnetic ranges, which could provide ultraviolet protection, for instance."

The idea is not at all far-fetched: team leader, Jean Pol Vigneron, has already shown that the optical properties of a beetle's carapace can be artificially reproduced. "His idealized model of the carapace could be used to define a manufacturing protocol that might even be extended to industrial scales," explained Sarrazin.

He also pointed out that the iridescence in the giant wasp has already been seen in the domestic pigeon, which has feathers with green and violet hues. "This is a consequence of natural selection and such natural 'devices' could be copied, and even improved, for technological applications."

The team now plans to study other insects in the same way.

The work was reported in arXiv.