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Dung Beetles Follow the Stars

The excrement-rolling bugs navigate by the light of the Milky Way
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The humble dung beetle makes its living rolling big balls of excrement to feed its offspring and itself. But this lowly occupation doesn't mean the insect doesn't have its eye on the skies—even when the sun goes down.

Recent research has shown that a species of ball-rolling dung beetles (Scarabaeus satyrus) uses strong light cues from the sun and moon to keep traveling in a straight path. Yet researchers at Sweden's Lund University and South Africa's University of the Witswatersrand noticed that even on clear, moonless nights, many dung beetles still managed to steer a straight path.

To see if the sky was serving as a guide, the researchers, who published their study online January 24 in Current Biology, designed specially crafted cardboard caps for their subjects. On a starry evening, they released capped beetles with their dung balls from a central spot in Vryburg, South Africa. As a test, other beetles were left uncapped, and a third group received transparent plastic caps. The beetles without caps and those with clear caps had standard, relatively straight paths: because competition among dung beetles for food is fierce, the insects prefer to flee in a straight line as soon as they roll their dung into a ball. Those with the obstructed views meandered far afield, however, and had much longer, inefficient trails.

To make sure that the stars were the only guiding landmarks, the researchers designed several more experiments. In one, they transported their beetles to the Johannesburg Planetarium. A close approximation of the night sky, including individual stars and the Milky Way, led to the more exacting navigation. If shown just the Milky Way, as a diffuse stripe of light, the beetles still made good time. But if the researchers took the Milky Way out of the picture and gave the beetles 18 bright “stars” to navigate by, they did not stick to their direct paths and took more than 50 percent longer to reach their destination.

“This clearly shows that the beetles do not orientate to a single bright ‘lodestar’ but rather to the band of light that represents the Milky Way,” the researchers note. Their findings may represent the first convincing demonstration of the use of the Milky Way for orientation in the animal kingdom.

Adapted from Observations at blogs.ScientificAmerican.com/observations

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