Why scarab beetles dance on a ball of dung

The ancient Egyptians would have nodded sagely: scarab beetles perform a dance to the sun atop a ball of dung. They're not worshipping a sun god, though: the beetles dance to orient themselves and – crucially – to roll their dung ball in a straight line.

Dung beetles were sacred in ancient Egypt, their dung-rolling linked with the nocturnal activity of Khepri, the god of the rising sun. Khepri was supposed to roll the sun through the underworld at night, pushing it over the horizon in the morning. Now Emily Baird of Lund University in Sweden and colleagues have shown that a diurnal dung beetle in South Africa (Scarabaeus nigroaeneus) uses celestial cues to ensure it keeps going in a straight line away from the dung pile.

Beetles collect dung from a pile and form it into manageable balls. Making a ball costs time and energy, and competition for dung can be intense, so it's best for a beetle not to hang around when it's got a precious new ball ready to roll.

"As a fresh dung pat can attract many beetles, it is necessary for individual beetles to try to avoid the others that may try to steal their ball," says Baird. "To do this, the beetles roll their ball away from the dung pile in the most efficient manner possible. That is, in a straight line."


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