Dancing dung beetles capture mental maps of the sky
With a twirl, a dung beetle trundles off in a straight line with its precious meal. But how does it know which direction to go? Belinda Smith reports.
Researchers from Sweden and South Africa, led by Lund University's Basil el Jundi, popped dung beetles under an artificial sky and saw the position of the Sun and light changed the direction the beetles rolled their meals.
They published the work in Current Biology.
Just before rolling a precious ball of dung, a dung beetle will usually crawl on top of the ball, spin around, then take off rolling the ball in a straight line.
That they use landmarks in the heavens to navigate has been known since 2003.
In 2013, researchers (including some involved with this most recent work) showed the beetles tend to get disorientated under cloudy skies. And at night, they can navigate by the light of the Milky Way.
"Other animals and insects also use the position of celestial bodies to navigate, but the dung beetles are unique," el Jundi says. "They are the only ones to take a snapshot where they gather information about how various celestial bodies, such as the sun, moon and stars, are positioned."
"They are the only ones to take a snapshot where they gather information about how various celestial bodies, such as the sun, moon and stars, are positioned."
When the beetles take in and process this information, and how much they use in their mental maps, hasn't been tested until now. In day time, do they solely rely on the Sun?
So el Jundi and his colleagues placed adult dung beetles (Scarabaeus lamarcki) and a ball of dung in an indoor arena. They controlled the position of the "Sun" – a green light – and polarised light patterns to make it appear more like the daytime sky.
The beetles' first roll was under the fake Sun and polarised light. When the researchers switched either the light or Sun off for the second roll, the beetles were still able to navigate.
But when the beetles rolled under the "Sun" only, then under the polarised light only, they headed off in random directions.
They then tested to see if the dance was integral to the mental map.
Indeed, they found a beetle that orientated itself on its first roll using the fake Sun, trundled off in random directions during their second roll when the Sun was switched off – even if they had polarised light.
This shows the dance is the point where dung beetles take their snapshot of the sky.
See the dung beetle's dance below: