How peacock spiders make rainbows on their backsides
Peacock spiders may be the world’s cutest arachnids. And they may be the only ones who are verified Youtube stars. They hail from Western Australia. These minute creatures are just five millimeters long. But their parts that make them so eye catching are their thoraxes. They are are covered with iridescent rainbows.
Those beautiful rainbow colors are the only display in nature that uses all the colors of the rainbow. That's according to Brandon Specktor at LiveScience. Now researchers have figured out how the little spider produces the rainbows.
There are two particular species of peacock spider. The first is the Maratus robinsoni, also known as the rainbow peacock spider. And the second is the Maratus chrysomelas. They have particularly notable displays.
A team of biologists, physicists and engineers came together to figure out just how the spiders produce their rainbow. They studied the scales on the spider’s thorax. They produce the impressive color. The team created micro-3D models of the scales to test how they worked. They used techniques like electron and light microscopy. They also used imaging scatterometry and optical modeling.
What they discovered is related to aviation. The rainbow color is produced by a specialized scale shaped like an airfoil or airplane wing. Parallel ridges on top of the scale act as tiny diffraction grating. They are able to divide visible light into its component colors. That's according to Nature Research Highlights. A slight curvature of the scale allows light to pass over more ridges. It separates the light into the colors of the rainbow even more effectively than if the scales were flat. The research appears in the journal Nature Communications.
It’s interesting to find out just how the spiders create their rainbows. But it is also giving scientists and engineers ideas for new ways to create such bright iridescent colors.
“As an engineer, what I found fascinating about these spider structural colors is how these long-evolved, complex structures can still outperform human engineering,” said Radwanul Hasan Siddique. He is a postdoc at Caltech. He is also and a co-author of the study. “I wonder how the spiders assemble these fancy structural patterns in the first place.”
This isn’t the first time lead author Bor-Kai Hsiung has investigated smartly colored insects. In 2015, he investigated the surprisingly numerous species of blue tarantulas in the world. He was a a grad student at the University of Akron at the time. Hsiung and his co-authors discovered that the blue colors in tarantulas was also structural—created by the manipulation of light instead of being produced by a pigment or coloring. This is much like the peacock spider rainbows. That was reported at the time by Ed Yong at The Atlantic.
But the blue coloring of the tarantulas is not iridescent or shiny. It is a muted blue. It might allow the arachnids to blend into shadows on the forest floor. This is a useful property. That's what Hsiung told Yong in 2015. By learning how the tarantulas produce matte colors, scientists could perhaps learn how to create long-lasting bright colors that don’t cause headaches.
“We usually don’t want colors to change over different viewing angles. It’s good eye candy but you don’t want to be living in a room with iridescent paint,” he said. “If we can mimic tarantulas and produce structural colors that are bright and non-fading, it might be useful for color displays on electronics, e-readers, TVs, or computers.”
The way the peacock spiders use structural colors to produce a rainbow also has lots of potential industrial applications. It could help make small optical spectrometers for space missions or could help produce wearable chemical detection systems. That's according to the press release.
It might also end up on your living room walls. Hsiung’s studies on the tarantulas and peacock spiders was partially sponsored by the paint company Sherwin-Williams. That's according to Katie Byrd at the Akron Beacon Journal. But its unlikely the colors will hit the shelves as “Tarantula Blue” or “Rainbow Spider Thorax.”