We humans like to think that that we're the only ones who figured out how to navigate using the stars. But as biologists from South Africa and Sweden recently discovered, the crafty dung beetle does it, too. This poop-obsessed insect uses the star-filled streak of the Milky Way to orient itself along a straight line — making it the only animal ever observed to use our galaxy for navigation. Intrigued, we talked to one of the researchers to find out more.
We contacted Eric Warrant, an Australian biologist now working at the University of Lund in Sweden. An expert on dung beetles, he has done previous work documenting the extraordinary talents of this insect, including its ability to see in the dark and orient itself with stars and the moon. But now, Warrant, along with his colleagues, have demonstrated that the dung beetle can navigate by using the Milky Way as well.
In the new study, which was published online today in Current Biology, the researchers showed that the dung beetle uses the milky band to get around — and it's the only animal now known to do so (not even birds do this, who are known to use individual stars for navigation).
"It is indeed the Milky Way streak of light that is seen — and this streak is very noticeable in the Southern hemisphere," Warrant told io9. He suspects that the beetles are probably not even capable of discerning individual stars, but are capable of picking up diffused light.
"That said, it's very likely that the beetles can see the brightest stars in the sky — they have quite sensitive compound eyes — but exactly how many remains to be determined." He says his team plans on studying this further — a future project that would look deeper into the dung beetles' physiological characteristics.
"In contrast," he says, "the Milky Way is a bright band of light made up of countless millions of stars, and this they can see and orient with respect to."
In previous experiments, Warrant's colleague Marcus Byrne discovered that the beetles climb on top of their dung balls to perform an orientation "dance" during which they locate light sources to use for orientation. He proved that dung beetles were relying on the moon and polarized light by putting "caps" on their heads which blocked light from reaching their eyes.
In the new study, Warrant, along with Marie Dacke and colleagues, showed that dung beetles lose their ability to transport dung balls along straight paths in overcast conditions. In a planetarium setting, however, the beetles were able to stay on track equally well under a full starlit sky — and importantly — a simulated sky showing only the diffuse streak of the Milky Way.
And indeed, navigation is crucial for dung beetles — and it's all about the big ball of crap they're desperately trying to protect.
"Dung is a precious resource for food," Warrant told us, "and male beetles invest much energy and time in creating and rolling a ball that will be used by a female to lay her egg within." It's an investment, he says, that's not lost on other male beetles — many of whom sit in wait for another beetle to create the perfect ball for them to aggressively steal.
"Thus once their ball is made, a dung beetle must get away from the fiercely competitive dung pile as quickly and as efficiently as possible," says Warrant, "and the best way to do this is in a straight line, in any direction." Inadvertently rolling back into the dung pile would likely prove disastrous. "This is why straight-line navigation is so important to these animals," he says.
Given the importance of the Milky Way to the dung beetle, we asked Warrant if light pollution might be causing a problem.
"Not at this stage, but this could become a serious issue for some species in some parts of the world in the future," he responded.
Looking ahead, Warrant and his colleagues will try to determine which neural circuits are responsible for this ability, and they'll do so by electrophysiologically recording the visual cells in the central brain of dung beetles.