The Mexican butterfly’s invisibility is due to small, individually arranged crystals located on the underside of its wings. The crystals provide the butterfly with its distinctive green color. The green coloration enables butterfly to hide from predators.
How this works has been a mystery to scientists, especially with understanding how the crystals grow and develop. An answer appears to have come from the University of Fribour and it all comes down to nanoscience.
Researchers have been studying the nanostructure located on the wing scales of the green hairstreak butterfly. The green hairstreak (Callophrys rubi) is a small butterfly in the family Lycaenidae. The undersides of the wings provide the illusion of being green, which is due to the diffraction of light on a lattice-like structure found within the wing scales. This provides excellent camouflage for the butterfly.
Investigating the wing structure, the researchers found that each wing scale was structured with nanocrystals. The structure was revealed through the use of electron and x-ray microscopy. The imaging showed the crystals, unlike most crystal formations, were not interconnected. Between each crystal was a regularly spaced point. Here what are termed gyroid photonic structures exist. The gyroids are three-dimensional structures first that partially pigmented and these are responsible for butterfly’s green color.
Further study revealed that the repetition of these nanostructures leads to a formation that is similar to the wavelength of visible light. This effect accounts for the optical property of the wings – a green color without any pigment. This arrangement makes the green hairstreak butterfly very unusual indeed. As well as camouflage it is thought the structures aid with signaling to other butterflies and with water repellency.
Speaking with Controlled Environments, lead researcher Dr. Bodo Wilts explains: “The unique structure found in these scales looks like it is still ‘growing’.” In addition he explains: “The results give insights into how butterfly wing cells develop, but could also provide inspiration for new nanoscale assembly techniques. The structures are not only precisely formed, but also developed under normal temperature and pressure conditions.
The results have been published in Science Advances. The research is titled “Butterfly gyroid nanostructures as a time-frozen glimpse of intracellular membrane development.”
