Beetles that roll dung balls in straight lines by orienting to the Milky Way. The first animals proven to use stars for navigation without tracking the sun.
An astronomer in the grass
In the savannas of southern Africa, the nocturnal dung beetle Scarabaeus satyrus performs an impressive feat of celestial navigation. After finding fresh herbivore dung, the beetle shapes it into a sphere, sometimes larger than itself, and rolls it away in a straight line. This linear escape is important for getting the valuable food resource away from the main pile, where intense competition from other beetles is guaranteed. To maintain this straight path without landmarks, the beetle looks to the sky. Before rolling, it often climbs atop its ball and performs a brief, pirouetting "dance." This maneuver is an orientation behavior, allowing the beetle to look at the sky for a reliable light source to use as a compass.
For decades, researchers knew these beetles could orient using the bright discs of the sun and moon. Studies also revealed they are sensitive to the polarization of moonlight, patterns of light created as it scatters through Earth's atmosphere that are invisible to human eyes. But a puzzle remained: the beetles still rolled in straight lines on clear, moonless nights. This observation led researchers from South Africa's University of the Witwatersrand and Sweden's Lund University to a remarkable hypothesis. They suspected the beetles were navigating by the faint, diffuse light of the entire Milky Way galaxy.
Experiments in a planetarium
To test the galaxy-navigation idea, researchers led by Marie Dacke and Marcus Byrne brought the beetles indoors. They placed the insects inside the Johannesburg Planetarium at the University of the Witwatersrand. By projecting different night skies onto the dome, they could control precisely what the beetles saw. The experiments showed that the beetles could navigate efficiently under a fully projected starry sky. Then, the scientists showed the beetles only the bright, hazy band of the Milky Way. The beetles continued to roll their dung balls in straight lines. When the Milky Way was removed, leaving only a few of the brightest individual stars, the beetles' paths became meandering and they took much longer to cross their circular arena.
These experiments, published in 2013, confirmed that Scarabaeus satyrus is the first animal known to use the Milky Way for orientation. Their compound eyes are too weak to resolve individual stars or constellations. Instead, they perceive the galaxy as a streak of light and orient themselves based on the light-to-dark gradient across the sky. Subsequent research has shown they can detect intensity contrasts as low as 13%, which is sensitive enough to distinguish the southern and northern arms of the galaxy. This ability provides a reliable compass even when the moon is not visible, allowing them to escape the chaos of the dung pile and secure food for themselves or a nursery for their young.
💡Fun Facts
To prove the beetles relied on celestial cues, researchers sometimes placed tiny cardboard "caps" on their heads, blocking their view of the sky and causing them to wander aimlessly.
The dung beetle's brain is smaller than a grain of rice, yet it can process complex celestial information for navigation.
A dung beetle can roll a dung ball up to 50 times its own body weight.
The ancient Egyptians revered the scarab beetle, associating its ball-rolling behavior with the god Khepri, who was said to roll the sun across the sky each day.
The research is primarily associated with the University of the Witwatersrand. Campus grounds are generally accessible during university hours, though specific labs are not open to the public.
Admission
Free to visit the university campus.
Accessibility
The University of the Witwatersrand campus in Johannesburg has paved walkways and is largely accessible.