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 true Youtube stars. They come from Western Australia. These are small creatures. They are just five millimeters long. What makes them so eye catching? 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. He works at LiveScience. Now researchers know how the little spider makes the rainbows.
There are two particular species of peacock spiders. The first is Maratus robinsoni. It is also known as the rainbow peacock spider. The second is Maratus chrysomelas. They have particularly notable displays.
A team of biologists, physicists and engineers came together to figure out just how the spiders make their rainbow. They studied the scales on the spider’s thorax. They make the vivid color. The team created micro-3D models of the scales. This let them test how they worked. They used many techniques. Those included electron and light microscopy. It also included imaging scatterometry. And it included optical modeling.
What they found is related to aviation. The rainbow color is made by a specialized scale. It is 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. It is even more effective than if the scales were flat. The research appears in the journal Nature Communications.
It’s interesting to find out just how the spiders make their rainbows. But it is also giving scientists and engineers ideas for new ways to make 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.” That's according to Radwanul Hasan Siddique. He is a postdoc. He is at Caltech. He is also a co-author. “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 looked at smartly colored insects. In 2015, he looked into the surprisingly numerous species of blue tarantulas in the world. He was a a grad student. He was at the University of Akron at the time.
Hsiung and his co-authors found that the blue colors in the tarantulas was also structural. It was made by the manipulation of light. This was instead of being made by a pigment or coloring. This is much like the peacock spider rainbows. That was reported at the time by Ed Yong. He was at The Atlantic.
But the blue coloring of the tarantulas is not iridescent. It also isn’t shiny. It is a dull blue. It might allow the arachnids to blend into shadows on the forest floor. This is a useful skill. That's what Hsiung told Yong in 2015. By learning how the tarantulas make matte colors, scientists could perhaps learn how to make 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. “Maybe 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 make a rainbow also has lots of likely industrial uses. It could help make small optical spectrometers for space missions. It 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 a paint company. That company is Sherwin-Williams. That's according to Katie Byrd. She works at the Akron Beacon Journal. But its unlikely the colors will hit the shelves as “Tarantula Blue” or “Rainbow Spider Thorax.”