Dung beetle on dung ball under the Milky Way; image courtesy of Emily Baird
The humble dung beetle makes its living rolling big balls of excrement to feed its offspring and itself. But this lowly occupation doesn’t mean the insect doesn’t have its eye on the skies—even when the sun goes down.
Recent research has shown that African ball-rolling dung beetles (Scarabaeus satyrus) use strong light cues from the sun and moon to keep traveling in a straight path. But researchers observing these beetles noticed something curious. “Even on clear, moonless nights, many dung beetles still manage to orientate along straight paths,” Marie Dacke, of Lund University in Sweden, said in a prepared statement. What else could the animals be using for guidance? The stars, of course.
“We were sitting out in Vryburg [in South Africa] and the Milky Way was this massive light source,” said Marcus Byrne, of Wits University and co-author on the new study, in a prepared statement. “We thought, they have to be able to use this—they just have to!” Their findings were published online January 24 in Current Biology.
Humans, of course, have long used stars for navigation. And some bird and seal species are thought to do so as well. The use of the Milky Way in particular has been suggested for some insects, spiders and vertebrates, but it has yet to be shown quite as convincingly as the researchers were able to demonstrate for these beetles, which have also recently been shown to engage in complex “dances” to orient themselves on top of their excrement orbs.
Dung beetle in experimental cardboard cap to block view of stars; image courtesy of Marcus Byrne
To see if the starry sky was really serving as such a lofty guide for these little bugs, researchers designed specially crafted cardboard caps for their subjects.
On a starry, moonless evening, researchers released capped-beetles with their dung balls from a central spot. The area was a flat sandy surface surrounded by a one-meter high, circular wall. As a test, other beetles were left uncapped and a third group received transparent plastic caps. The cap-less beetles and those with clear caps had standard, relatively straight paths. But those with the obstructed views meandered far afield and had much longer, inefficient trails.
