Peacock spider’s radiant rump comes from teeny tiny structures

Pigments produce reds and creamy yellows, while nanostructures turns other parts blue

The peacock spider gets its blue bling from small reflective structures.

JÜRGEN C. OTTO (FLICKRYOUTUBE)

Male peacock spiders know how to work their angles and find their light. These arachnids are native to Australia. And males are quite a sight to see. They rely on the vibrant hues coloring their hind ends to attract females. A guy will raise skyward  his derriere — or, more accurately, a flap on his hind end — and shake it catch the gals’ attention. Now scientists have figured out where his fancy colors come from.

Doekele Stavenga is an expert in optics at the University of Groningen in the Netherlands. He and his colleagues started by collecting peacock spiders. They found these specimens of Maratus splendens in a park outside Sydney, Australia. Then they zoomed in on the scales that cover the spiders’ rears.

The team used microscopy, spectrometry and other techniques to image the scales. The red, yellow and cream scales rely on two pigments to reflect their colors. (Pigments are chemicals that reflect light to produce colors.) Even the white scales contained low levels of pigment. Spines lining these scales scatter light randomly. That gives them slightly different hues when viewed from different angles.

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Scientists made close-up images of a peacock spider’s rear end with a scanning electron microscope. The results reveal the miniature scales that produce colors in the hairlike scales that adorn the spider: white (left), red or yellow (middle) and blue (right; whole structure at right, detail at left).D.G. STAVENGA ET AL/J. R. SOC. INTERFACE 2016

Blue scales worked differently. They’re transparent and lack pigment. Instead, the shape of the scales cause them to reflect iridescent blue and purple hues. Each scale resembles a sac or a peapod. It is lined with tiny ridges on the outside. Inside there’s a layer of threadlike fibers. The spacing of those fibers may determine whether scales appear more blue or more purple.

Whether peacock spiders’ eyes can actually see these posterior patterns is not certain, the researchers say. Species of jumping spiders can see at least three color ranges, just as humans do. So it seems unlikely that such vivid, come-hither dance moves play out in only black and white.

The findings appear in the August Journal of the Royal Society Interface.

A male peacock spider’s rear end is adorned with bright colors. He uses that decoration in a dance aimed at catching the eye of more drably colored females. Peacockspiderman (JÜRGEN C. OTTO)

Helen Thompson is the associate digital editor. She has undergraduate degrees in biology and English from Trinity University and a master’s degree in science writing from Johns Hopkins University.

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