Meet the Dung Beetle, Keen Navigator by Starlight

dung beetle

Dung beetles use starlight to navigate at night. (Photo credit: Cathy Withers-Clarke/Shutterstock)

It’s a disgusting way to live, but dung beetles do it … and thereby deserve their unenviable name. Males of the species seek out steaming piles of manure, descend on them, shape some of the smelly stuff into balls, and roll them away from chaos of the pile, hopefully attracting a mate along the way. If successful, the happy couple then bury the dung ball in a safe place to serve as food for their future offspring. That’s dedicated parenting! More significantly, it’s an activity requiring a fairly keen sense of direction, as the tiny bug wants to be sure it’s taking the straightest path away from the swarm of others of its kind just waiting to steal the prized ball of dung away from it. The dung beetle’s ability to move in a straight line has long fascinated scientists. They figured it must come from the bug’s ability to sense a pattern of polarized light around the sun invisible to other animals. What was puzzling was that, let’s face it, dung collection is something best done in the dead of night. Many dung beetles do collect at night. Without the sun, however, how could those working the night shift ever get the job done?

Like most who study these insects, biologist Eric Warrant of the University of Lund in Sweden thought night owl beetles must take their cues from the light of the moon. The light is much less intense, of course, but it also has a polarization pattern that beetles could be sensing. So he and his team went to South Africa to collect some dung, use it to lure the nocturnal beetle Scarabaeus satyrus, and, once and for all, figure out just how these insects roll.

As expected, the beetles proved extremely capable of rolling their dung by the light of the moon. However, on moonless nights, the beetles showed no indication of being any less capable of keeping their rolls on the straight and narrow. But how? Could it be they were not following the moon, but the stars? And, perhaps, not just the stars, in general, but the Milky Way galaxy, in particular?

To test the idea, Warrant and his team took the beetles to the Johannesburg Planetarium and simulated conditions with both a full starlit sky and one illuminated only by the Milky Way. In each case, the beetles could move in straight lines, thus apparently confirming the Milky Way hypothesis. To be completely sure, the scientists blindfolded the beetles (i.e., put tiny cardboard shades over their eyes) and observed that only then would the bugs wander about aimlessly in the light. While the Milky Way is most prominent in the Southern Hemisphere, many believe that most other dung beetles around the world, and possibly other insects, may be using it as their guide.

As the researchers refined the parameters of the study, however, they realized something even more amazing. It really didn’t matter how the stars were placed in the sky; the beetles kept rolling on the straight and narrow, even if sky conditions were artificially changed from night to night. The only conclusion was that the beetles weren’t relying on a preconceived idea of what the night sky looks like, but instead taking a “snapshot” of the sky (most likely doing so as they danced upon their balls of dung) and then using that picture as a comparison map as they rolled it away. During transit, they compare the stars above them with the snapshots they took and, thereby, keep themselves oriented.

Perhaps what most impressed the University of Lund researchers was the relative efficiency of the process. The single snapshot means the beetles do not need to continually retrieve information. The single picture is enough and, providing the sky doesn’t change while they’re in transit, the beetles can efficiently use it to determine where they are always. Other insects are known to use the stars for navigation. Ants are also known to take snapshots of their surroundings. The dung beetle seems to be the only insect so far that combines both a photographic brain and an old seafarer’s ability to navigate by starlight. The hope is that we might be able to learn from these unusual insects to produce better navigation systems, like for those in self-driving cars.

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