If you can look past the hair, oversized fangs, and profusion of eyes and legs, tarantulas are actually quite beautiful. There are Halloween-ready specimens with deep black bodies and bright rust accents; there are lemon yellows, car-show worthy chromes, and a variety of electrifying blues. It’s the nature of these blues that set tarantulas apart from other animals and are of interest to biologists and materials engineers alike.
Arielle Duhaime-Ross at the Verge spoke with the authors of a study published last week in Science Advances examining the microscopic structure and evolutionary origins of tarantulas’ idiosyncratic coloration.
Metallic blues are not a tarantula-exclusive color—they can be found on many beetles and butterflies, and even on common crows in certain lighting. That “certain lighting” bit is the key. You’d be forgiven for not noticing, but the blue of tarantulas is not iridescent—that is, it doesn’t change depending on the viewing angle. “That’s a big differentiator from the highly iridescent structural colors seen in most birds, butterflies, and beetles,” Duhaime-Ross writes. She goes on to quote Todd Blackledge, one of the authors and an arachnologist at the University of Akron. “This potentially makes tarantulas a really important model for designing color-producing technology for TVs, phones, and other devices that are easier to look at.”
The iridescence that usually goes hand-in-hand with structural color is one of the big obstacles in developing structural color technology. Most of the artificial color in our world is pigment-based. Pigments are materials which absorb certain wavelengths of light. Chlorophyll in plants, for instance, is a pigment that preferentially absorbs every wavelength of light except green—and it’s the reflected light that gives leaves their verdancy. We use pigments in our paints, our clothing, even our foods—but pigments tend to degrade over time and don’t seem able to achieve the same intensity as structural colors.
In November, scientists succeeded at creating a soft material with a structural color that changes from red to green to blue with increasing temperature, modeled on the way chameleons can change the colors of their skin. They dynamically alter the spacing of nanocrystals in their skin, which in turn changes the way their skin reflects light. The results are dramatic color shifts unlike any other terrestrial animal. The researchers achieved a similar effect using silica particles suspended in a gel.
Earlier this fall, Katherine Derla reported on a new super-black material for Tech Times made using a microscopic structure of carbon nanotubes on top of a nanoparticle sphere—it absorbs up to 99 percent of the visible light. “The resulting color is so dark,” Derla writes, “that the human eye is unable to see it. People who have laid their eyes on the materials said it felt as if they were looking deep into a bottomless abyss or black hole.”
The researchers got their inspiration from the ultrawhite Cyphochilus genus of beetle, reverse engineering its structural color to create their material. (Beetles are a popular study subject for their structural color; here’s MIT Technology Review writer Kristina Grifantini’s 2009 story about green beetles.)
Duhaime-Ross and the tarantula researchers acknowledge that any applications based on their tarantula research are a long way off. Though they now have a better idea of which microscopic structures are responsible for the brilliant blue coloration of these animals, they still don’t understand how to reproduce it. The tarantula study is best seen as part of a larger effort to better understand how plants and animals get their brilliant coloration—so that materials scientists can copy it.