You know that moment when you realize that in every unloved corner of the animal kingdom, there’s an ant or a bee or a beetle standing on its head and pushing a boulder of crap that has a better sense of direction than you do?
Dung beetles are named for their favorite food source. Upon finding, say, a fresh cowpile, the dung beetle cuts off a chunk, shapes the specimen into a ball bigger than its body, and then rolls the ball away to a new location. Unlike Sisyphus, the dung beetle pushes its burden by facing backward and rolling the ball with its hind legs. Once it finds a nice spot to settle down with its ball of dung, the beetle buries the ball for safekeeping and gradually consumes it.
The beetle’s journey away from the poop pile is punctuated by another surprising behavior. Periodically, the dung beetle stops pushing, climbs on top of its dung ball, and spins around. Scientists generously refer to this behavior as “dancing.”
A group of researchers from Sweden and South Africa hypothesized that the dancing behavior is really a way for the dung beetle to get its bearings. The beetles are known to have good orienteering skills; but unlike other animals that use environmental cues to navigate homeward, the dung beetle’s goal is to get far away from that big pile of poop. If it stays too near to the source, or accidentally circles back to where it started, it risks being attacked and robbed of its prize by other dung beetles.
Dung beetles always travel in a very straight line away from where they found their poop. And their ability to navigate relies on clues from the sky, such as the sun, the moon, and polarized light patterns. To find out whether spinning around on top of its dung ball is a way for the beetle to check its bearings and maintain a straight path, the researchers put a few dozen beetles and their balls through an obstacle course.
The first step was simply to film the dung beetles, which had been gathered from the wild in South Africa, as they built and began rolling their balls. A majority of the beetles climbed on top of their dung balls and “danced” before they even started rolling. This might have been when the beetles chose the bearings they would use for the rest of the trip. (Though almost 40 percent of the beetles did not dance at this stage, the researchers note that the beetles spend a lot of time on top of the ball while they’re forming it, and might get their bearings during this stage instead.)
Then the obstacles began. The beetles faced challenges that were meant to simulate the real difficulties of rolling a dung ball along a bumpy surface, say, or a grassy slope. First, beetles were steered into an open-roofed tunnel with a closed door at the end of it. Upon bumping into the solid object, every beetle climbed at once onto its dung ball and spun around as if reassessing its path. (“It should be noted,” the authors write, “that all beetles continued to roll straight into the closed door after performing a dance.” The beetles may have been confirming their bearings, but they apparently weren’t interested in a new course.)
When sent through a different tunnel that veered them off to the left or right of their original course, most beetles performed a dance. When put in a swiveling tunnel and quickly spun 180 degrees, only about half the beetles noticed and did a dance—but almost all of those beetles then turned back in the correct direction.
However, when the swiveling tunnel was covered so the beetles couldn’t see the sky, almost none of them danced. They seemed to be responding only to visual cues, not to the feeling of being spun around. To further test the beetles’ reliance on sight, the researchers used a mirror to make it seem like the sun had shifted 180 degrees. In response, more than half of the beetles stopped and did a dance, and most of those beetles switched direction: changing the angle of the sun had convinced them to go the other way.
The authors think there’s more to be learned about dung beetle dancing by studying the non-dancers in various situations. Are those individuals relying on different cues, such as light polarization instead of the location of the sun? Or are they just not the sharpest pooper-scoopers in the shed? Either way, the dung beetles that make it to safety with their pre-digested treasures have a skill set that should make us humans feel like, well, number two.
Image: Wikimedia Commons/Dewet
Baird, E., Byrne, M., Smolka, J., Warrant, E., & Dacke, M. (2012). The Dung Beetle Dance: An Orientation Behaviour? PLoS ONE, 7 (1) DOI: 10.1371/journal.pone.0030211
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1 day ago in The Phytophactor