Magazine article Science News

Mood Bugs: Beetle Changes Color in Fluid Fashion

Magazine article Science News

Mood Bugs: Beetle Changes Color in Fluid Fashion

Article excerpt

Color-changing animals, such as chameleons and squid, typically alter their hues when nerve signals or hormones spur pigment cells in their skin to expand or shrink. The Panamanian golden tortoise beetle, however, changes color dramatically from metallic gold to matte red by a very different method, researchers report. It uses its body fluid to structurally alter the reflectivity of its shell--a trick that could one day be built into devices that would optically signal the presence of a liquid.

This color-change method is "something very rare" says lead author Jean Pol Vigneron of the University of Numar in Belgium.

The 8-millimeter-long beetle, Charidotella egregia, sports a transparent shell made of the biopolymer chitin, which forms insect exoskeletons. The shell normally reflects a metallic-gold color, but that sheen fades to reveal a red pigment when the beetle is disturbed.

Using electron microscopy, Vigneron and his colleagues found that the shell has a three-tiered structure, with each tier consisting of a number of closely packed layers. Each of the tiers--the thickest is at the bottom, the thinnest at the top--reflects a particular wavelength of light, and those wavelengths combine to produce the gold coloration. Beneath the tiers is a layer of red pigment.

The researchers' high-resolution images also revealed randomly placed patches of nanosized grooves or channels in the layers that make up each tier. When the beetle's body fluid fills these channels, the layers become smooth. …

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