Like a gem-studded overcoat, the diamond weevil’s jet-black wings are covered by pits filled with sparkling, rainbow-colored scales. Researchers have studied these “diamonds” since the weevil’s discovery in the early 19th century but, until recently, no one knew know how the scales reflected so much light. A new high-tech investigation reveals the diamonds are just that: chitin in a diamond-type arrangement that's optimized to throw off brilliant greens, yellows and oranges. What most people call diamonds are made of carbon, but other materials can take on the same crystal structure, called diamond cubic. “Materials scientists could look to these scales to inspire new materials, but we don’t yet know how they are made,” said biophysicist Bodo Wilts of the University of Groningen, co-author of a Dec. 21 study of the scales in Journal of the Royal Society Interface. “We’ve got some catching up to do,” Wilts said. “The nature-produced tiny structures are far beyond any human designs.” The scales are a type of three-dimensional crystal, called a photonic crystal, which is much like an opal. Each kind of photonic crystal reflects a specific wavelength of light at a specific orientation. Other crystals lacking a regular 3-D structure, meanwhile, aren’t as brilliant or iridescent. Wilts’ team used a battery of tools to investigate the photonic studs the inch-long weevil, the Brazilian species of which is known as Entimus imperialis (pictured above). Follow along in this gallery.

Rainbow Pits Under an optical microscope, each one of dozens of pits lining a diamond weevil’s wings is filled with hundreds of teardrop-shaped scales. The scales are made of chitin, a biological polymer found everywhere in the animal kingdom, from insects to crabs and even mushrooms. “They're small, but the chitin makes them very tough,” Wilts said.

Multicolor Teardrops Further optical magnification shows how each scale is divided into sections of iridescent colors. Wilts said that, as the angle of light changes, so do the colors bouncing of the scales. Each scale is about 100 microns long, roughly equivalent to the thickness of a strand of human hair, 50 microns wide and 5 microns thick.

Ridges and Valleys A scanning electron microscope shows hints of a repeating crystal structure, primarily striations or ridges. For decades, researchers who looked at diamond weevils under microscopes suspected the striations themselves -- not the material they were made of -- were responsible for the rainbow of colors. “They surely didn’t have the right tools,” Wilts said. “They didn’t have the electron microscope or advanced optical technologies.”

Photonic Waffle The details of the diamond weevil’s photonic crystal structure become more evident under the powerful gaze of a scanning electron microscope. In this image, the scale is viewed edge-on, like the edge of a piece of paper. The waffle-like layer is about 5 microns thick (the scale bar, bottom right, represents 2 microns).

Scatterogram Analysis For highly regular and repeating photonic crystals, shining a very small but intense point of light can betray their superstructure. A glass pipette (black bar, left) holds a diamond weevil scale at center. When a very focused 50-micron-wide point of white light hits the scale, it sprays color onto a camera sensor. The patchy colors can then be analyzed to reveal the most basic unit of the crystal (red shape, right). In this case, the chitin crystals take on a regular arrangement of hexagons and squares (gray 3-D object, right).