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Dung Beetles Follow the Milky Way

25 January 2013

You might expect dung beetles to keep their "noses to the ground", but they are actually incredibly attuned to the sky. Indeed, a report in the 24 January Current Biology, a Cell Press publication, shows that, even on the darkest of nights, African ball-rolling insects are guided by the soft glow of the Milky Way.

While birds and people are known to navigate by the stars, the discovery is the first convincing evidence for such abilities in insects, the researchers say. It is also the first known example of any animal getting around by the Milky Way as opposed to the stars.

"Even on clear moonless nights, many dung beetles still manage to orientate along straight paths," said Marie Dacke of 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."

Dacke and her colleagues found that dung beetles can transport their dung balls along straight paths under a starlit sky, but lose the ability under overcast conditions. In a planetarium, the beetles stayed on track equally well under a full starlit sky and one showing only the diffuse streak of the Milky Way.

That makes sense, the researchers explained, because the night sky is sprinkled with stars, but the vast majority of those stars should be too dim for the beetles' tiny compound eyes to see.

The findings raise the possibility that other nocturnal insects also use stars to guide them at night. On the other hand, dung beetles are pretty special. Upon locating a suitable dung pile, ball-rolling dung beetles shape a piece of dung into a ball and roll it away in a straight line. That behaviour guarantees them that they will not return to the dung pile, where they risk having their ball stolen by other beetles.

"Dung beetles are known to use celestial compass cues such as the sun, the moon and the pattern of polarised light formed around these light sources to roll their balls of dung along straight paths," Dacke said. "Celestial compass cues dominate straight-line orientation in dung beetles so strongly that, to our knowledge, this is the only animal with a visual compass system that ignores the extra orientation precision that landmarks can offer."

Contact:
Marie Dacke
marie.dacke@biol.lu.se
Phone: +46 46 738 128798

Media Contact:
Lena Björk Blixt
Lena.Bjork_Blixt@science.lu.se