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The dung beetle as celestial navigator

Only humans, birds, and seals are known to navigate using stars. But the dung beetle does use the Milky Way to chart its path, say scientists.

By Joseph CastroLiveScience.com / January 25, 2013

Dung beetles have been shown to use the Milky Way to navigate.Researchers have known for several years that the inch-long insects use the sun or moon as fixed points to ensure they keep rolling dung balls in a straight line - the quickest way of getting away from other beetles at the dung heap. Pictured here, a South African dung beetle.

REUTERS/Marcus Byrne/University of the Witwatersrand

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Despite having tiny brains, dung beetles are surprisingly decent navigators, able to follow straight paths as they roll poo balls they've collected away from a dung source. But it seems the insects' abilities are more remarkable than previously believed. Like ancient seafarers, dung beetles can navigate using the starry sky and the glow from the Milky Way, new research shows.

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"This is the first time where we see animals using the Milky Way for orientation," said lead researcher Marie Dacke, a biologist at Lund University in Sweden. "It's also the first time we see that insects can use the stars."

After locating a fresh pile of feces, dung beetles will often collect and roll away a large piece of spherical dung. Last year, Dacke and her colleagues discovered the beetles climb on their dung balls and dance around in circles before taking off. This dance is not one of joy, however; the insects are checking out the sky to get their bearings.

"The dorsal (upper) parts of the dung beetles' eyes are specialized to be able to analyze the direction of light polarization — the direction that light vibrates in," Dacke told LiveScience. So when a beetle looks up, it's taking in the sun, the moon and the pattern of ambient polarized light. These celestial cues help the beetle avoid accidentally circling back to the poo pile, where other beetles may try to steal its food, Dacke said. [Photos of Dung Beetles Dancing on Poop Balls]

In addition to these cues, Dacke and her team wondered if dung beetles can use stars for navigation, just as birds, seals and humans do. After all, they reasoned, dung beetles can somehow keep straight on clear, moonless nights.

To find out, the researchers timed how long dung beetles of the species Scarabaeus satyrus took to cross a circular arena with high walls blocking views of treetops and other landmarks. They tested the insects in South Africa under a moonlit sky, a moonless sky and an overcast sky. In some trials, the beetles were fitted with cardboard caps, which kept their eyes to the ground. Overall, the beetles had a difficult time traveling straight and took significantly longer to cross the arena if caps or clouds obstructed their view of the sky.

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