Move over, Lawrence of Arabia: Scientists have discovered dung beetles that gallop through the desert like a horse.
The team was studying how three species of flightless dung beetles that live in coastal South Africa and Namibia navigate, when someone noticed a beetle hopping in a peculiar way. (Also see “Dung Beetles Navigate Via the Milky Way, First Known in Animal Kingdom.”)
“We were very surprised when we saw the first beetle—we thought he was a bit disabled, [wondering], ‘Did someone step on him?’” said study leader Jochen Smolka, a biologist at Sweden’s Lund University.
But when the team took high-speed video, they discovered that galloping was widespread among the three species. To gallop, a beetle propels its body forward while at the same time stepping with both middle legs and both front legs, and dragging its two back legs behind. (That’s not unusual: Dung beetles often use their back legs as a cargo sled, loading them up with dung and plant material.)
“What it always reminds us of is butterfly swimming—you’ve got this strong forward motion,” noted Smolka.
But the scientists were confused. The roughly three million other insect species on Earth walk with variations of a tripod gait, which means holding one stable triangle of legs steady while swinging the opposite triangle forward.
Why would these beetles have a gait so radically different from the most widely used walking style on our planet?
Theories in Motion
First, the team wanted to find out if galloping was faster than the usual gait, so they studied video footage of the beetles’ two speeds. Oddly, their analysis revealed that galloping is slower. (Play “Dung Beetle Derby” on the National Geographic Kids website.)
“We are still puzzled by it—we still don’t know why they’re doing this,” said Smolka, whose study appeared October 21 in Current Biology. But the team has a lot of theories that they plan to examine. Among them:
—The beetles are conserving energy. It may be that galloping is less physically taxing than walking for the beetle. For instance, the galloping gait is a bit like rowing with two oars simultaneously, which is more efficient than rowing with multiple oars at different times.
—Galloping points them in a straight line. If the gallop is indeed more efficient, perhaps it also helps the insect move in a straight line, which simplifies its journey to and from its burrow. Unlike the better-known dung-rolling beetles, these three species collect small pieces of dung and then take them back to their burrows. (Related: “Dung Beetles’ Favorite Poop Revealed.”)
—Gallops are easier to count. To get home, the beetles count their steps to and from their burrow—similar to the behaviors of fiddler crabs and ants. Since galloping requires fewer steps, perhaps the streamlined gait is easier to count.
—The beetles are avoiding the hot sand. This theory hasn’t been properly tested, but it seems unlikely since the insects live in deserts that aren’t terribly hot, say 104 degrees Fahrenheit (40 degrees Celsius), and dung beetles that live in much hotter deserts don’t gallop.
—Galloping confuses prey. These beetles are eaten by ground chameleons, and one “crazy theory” is that the galloping confuses chameleons into thinking a beetle is not a beetle at all—allowing it to, well, gallop away into the sunset.