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Monday, January 28, 2013
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Steered by stars

The humble dung beetle is the first insect known to navigate by the stars. Like sailors of old and Saharan nomads, it can orientate itself by watching the sky.

On clear nights, a myriad of stars shine over the deserts and savannahs of Africa where the dung beetle, or scarab, makes its home. While the beetle's compound eyes are probably too weak to see individual stars, it uses the light of the Milky Way to keep it on a straight course, scientists have found.

The beetles feed on animal dung, which they fashion into a ball and roll to a safe spot where it is less likely to be stolen. Rolling the ball in a straight line ensures they do not circle back to the dungheap, where other scarabs might have gathered.

Scientists wondered how they were able to do this in the dark. "Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths," said Dr Marie Dacke from Lund University in Sweden. "This led us to suspect that the beetles exploit the starry sky for orientation - a feat that had, to our knowledge, never before been demonstrated in an insect."

Dung beetles also use the sun and moon as compass cues.

Field experiments on a South African game reserve showed that the beetles were able to roll their dung balls along straight paths under starlit skies, but not in overcast conditions.

The beetles performed just as well when only the glow of the Milky Way was visible as they did under a full sky of stars.

Previously, only birds, seals and humans were known to navigate by the stars.

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