Call it a new twist on catching some rays: One species of dung beetle uses sunlight to steer its balls of poop, a new study says.
The dung beetle Scarabaeus lamarcki can roll poo balls in a straight line, which helps the insect move the precious ball away from the larger dung heap more quickly and bury it safely underground, where it serves as food. (That’s no small feat, especially when you consider that this blogger is still managing the art of walking and chewing gum.)
Biologist Marie Dacke, of Sweden’s Lund University, was interested in figuring out how S. lamarcki and other dung beetle species could successfully navigate and steer their dung in the right direction. (Also see “Can Dung Beetles Battle Global Warming?“)
A 2013 study by Dacke and colleagues showed that dung beetles could navigate using the Milky Way—the only species known to date to manage such a trick.
But S. lamarcki is only active during the day, which means it doesn’t use the Milky Way or anything else in the night sky to navigate.
From previous research, Dacke knew that when the sun is high overhead, it’s much harder for beetles to use the sun to orient themselves and figure out which direction to move. The big question for Dacke was whether the beetle also knew this.
Dung Beetle Directions
So Dacke and colleagues built an outdoor arena in South Africa where the beetles lived where they watched how dung beetles rolled their dung.
The team tested the beetles’ navigation skills at different times of day: At dawn and dusk, when the sun was low on the horizon; at noon, when the sun was high in the sky; and at mid-morning and mid-afternoon, when the sun was somewhere in between. (Watch a video of an African dung beetle at work.)
They also simulated a cloudy day by blocking the sun with a piece of wood, and switched the location of the sun by using a mirror to see if this would cause the beetles to switch direction.
The results showed the dung beetles made the fewest navigation errors when the sun was near the horizon, and the most errors at high noon and when the sun was blocked.
When the sun is lower on the horizon, Dacke said, it’s easier for the beetle to determine which direction it’s headed because the insect orients itself by keeping the sun on the same side of its body as the direction it’s traveling.
When the sun is directly overhead, this navigation technique doesn’t work very well because the sun would be shining on the beetle’s back.
The beetles were obviously using the sun to navigate, but they were also able to supplement with other environmental cues when it was cloudy or it was harder to tell direction from the sun’s location.
“It’s as if the beetles knew the sun wasn’t always reliable,” said Dacke, whose study was published recently in the journal Philosophical Transactions of the Royal Society B.
This shows that a good biological compass needs to be dynamic and flexible, rather than purely hardwired, she said.
So why go through all this trouble for a pile of poop? It may seem gross to us, but to dung beetles and a host of other species, this mountain of feces is really a giant smorgasbord—and getting a ball away from the chaotic dung pile is crucial. (Related: “Dung Beetles’ Favorite Poop Revealed.”)
“The competition is surprisingly intense,” Dacke said.
Some species of dung beetle will simply find the pile of poo and tuck in, eating directly from the steaming buffet. This option, however, isn’t without its risks. Besides increasing the chances that you will become dinner yourself, eating out in the open also means that other species could steal your lunch, leaving you with nothing.
A group of dung beetles known as the ball rollers have found an elegant solution to this problem. Using their head and front legs, these beetles, which includes S. lamarcki, form the dung into a ball and roll it in a straight line away from the dung heap.
“It’s a remarkably simple solution,” Dacke said. “As long as the beetles keep moving in a straight line, they won’t end up back at the dung pile.”
Which is not where you will find me.