We may not be partial to dung, but to dung beetles, poo is a hot commodity that a bigger beetle is sure to try to steal if it can. The beetles therefore roll their dung into balls as quickly as they can and leave the scene via the shortest possible path--which is a straight line. Dacke and her colleagues wanted to know how the beetles were able to navigate in such straight lines. That’s where the little hats came in.
The scientists used cardboard hats to prevent some of the insects from looking upward.
Credit: Eric Warrant
They then released the beetles with their dung balls into the center of a large circular area and timed how long it took the insects to reach the edge. All the beetles obligingly scurried along until they reached an edge, however, the beetles that could not see the sky took considerably longer, having followed a more meandering path.
The paths of various beetles from the center to the edge.
A) when they could see the starry sky
B) when they could not see the sky
Current biology : CB, 23 (4), 298-300 PMID: 23352694.
At night, the beetles followed the straightest path if they could see a full moon, but were almost as efficient under a moonless starry sky. With no view of the sky at all, the beetles took at least three times longer to reach the edge, despite traveling at the same speed.
Here’s where it gets even better. To fine tune exactly which celestial cues the beetles were using, the researchers repeated their experiments--in the Johannesburg Planetarium. Yes, folks, if you ever get the chance to attend a planetarium show in Johannesburg, you’ll know that a dung beetle beat you to it.
The beetles navigated nearly as well whether they were ‘under’ a complete starry sky or just a diffuse streak of light representing the Milky Way. In other words, the beetles were able to orient themselves using only the Milky Way. Not surprisingly, this is the first description of an insect navigating by way of the Milky Way.
You can hear more about this story on this week’s episode of Skeptically Speaking, starting at 45:00.