Science News

Dung Beetles Navigate by the Light of the Milky Way

Thu, 24th Jan 2013

Ben Valsler

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Dung beetles are remarkable creatures.  Not only does their way of life supply food from someone else’s waste, but recent research has shown that their dung balls keep their feet cool on the hot desert sands.

dung beetleBut now, research published in the journal Current Biology also shows that Dung beetles navigate by the light of the Milky Way, becoming the first insects known to use the night sky in this way to orient themselves.  In fact, it’s the first evidence of any animal using the diffuse light from the whole Milky Way, rather than the stars themselves, as a navigational aid.

Dung beetles find a fresh pile of dung, take a pinch and roll it into a ball.  They then must travel in a straight line away from the pile, or risk coming back round to it and having their dinner stolen.  Under a starlit sky, they retain this ability and navigate a straight path.  However, when it is overcast, and the stars are obscured, they lose their navigational skill.  This inspired Marie Dacke and colleagues from Lund University and the University of Pretoria to design a series of experiments to find out how the beetles know which way to go.

They manufactured tiny cardboard caps, much like the blinders on race horses, to obscure the beetles’ views of the sky.  This made a significant difference to the route the beetles would travel.  Even when a curtain was erected to block out all local landmarks that could be used for navigation, the most significant factor was their view of the sky.

To determine exactly what aspects of a starry sky were providing the navigational cues, they next took their volunteer beetles to the Johannesburg Planetarium, where they had full control over the sky overhead.  This showed that the Milky Way itself, visible as a diffuse streak of light, was the most important factor, and the presence of individual stars made little difference.

Although this is, so far, a unique observation, the authors argue that there’s no reason to think it’s a unique strategy, citing some evidence of night time orientation in cricket frogs and stating:

“Although this is the first description of an insect using the Milky Way for their orientation, this ability might turn out to be widespread in the animal kingdom.”



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That's fascinating and also raises another question for me.  I have always thought dung beetles roll their dung away with their hind legs (rs in the air so to speak :-) ).  If that's the case and I haven't got that wrong, what do they navigate with?  Are their eyes positioned in such a way that they can see the sky in that position or do they have a photo-receptive backside? Minerva, Tue, 29th Jan 2013

Hmmm, that could be handy.

The Dung Beetle has compound eyes, so while it may have its bum in the air, it can see pretty much all around it. Just as well if you plan to navigate by the stars, but equally handy when you consider that a dung beetle which takes its eye off the ball (so to speak) will likely find another dung beetle pinching his balls. You'd think that just one elephant would provide enough ........ erm....... dung to satisfy all the local residents, even so a dung beetle will readily do a runner with another dung beetle's balls. Don_1, Wed, 30th Jan 2013

Thanks Don-its fascinating stuff.  Presumably then seeing ahead is not a necessity so is there any reason they use their back legs rather than their front legs to roll the dung?  Minerva, Wed, 30th Jan 2013

Looking at the photos, it appears as if the beetles have 2 front legs and 4 back legs.  This may in fact be common among insects.  It likely is easiest to roll the ball using the 4 back legs, while waking on the 2 front legs. 

Obviously evolution led to their niche.  But, assuming an ancestor also had 6 legs, it may have been easier to adapt to using the 4 back legs to roll the ball, rather than adapting to walking on one pair of rear legs, and using the other pair of front legs and rear legs together to roll the ball. CliffordK, Wed, 30th Jan 2013

I see - thanks.  I wonder how they experience the Milky in I wonder if they sense its a great distance away......? Minerva, Thu, 31st Jan 2013

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