QuestionSacred scarab
How Do Dung Beetles Navigate? Steering by Sun and Milky Way
Ball-rolling dung beetles navigate with the sky. After shaping a dung ball, a beetle climbs on top, turns to take its bearings, then rolls in a straight line using the sun, the pattern of polarized light around it, the moon and, in at least one African species, the band of the Milky Way. Landmarks on the ground play almost no part.
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Why do dung beetles need to roll straight?
A ball-rolling beetle is not heading home. It is trying to get away from the dung pile, where other beetles crowd in and try to steal finished balls. The fastest way out of a crowd is a straight line: a beetle that wandered in circles would end up back among the thieves. So the beetle picks a random direction and sticks to it until it finds soft soil to bury its ball, often several meters away.
This is a simpler job than the homing of bees and ants, which must find their way back to a nest. The beetle only needs a compass, not a map. You can read more about the reasons for rolling in why dung beetles roll balls.
The dung beetle dance
Before setting off, a ball roller climbs on top of its ball and rotates on the spot, a behavior scientists call the dance. A 2012 study of the South African beetle Kheper nigroaeneus found that beetles also dance whenever they lose control of their ball, are pushed off course, or see the light cues around them change.
Researchers think the dance is the moment the beetle takes a “snapshot” of the sky, storing the position of the brightest light and the pattern of polarized light. While rolling backward with its head down, it then keeps that sky picture in the same position on its eyes. Like many insects, dung beetles have a special strip along the upper edge of each eye that is sensitive to polarized light, which suits this upward-looking navigation.
Steering by the sun and polarized light
By day, ball rollers use the sun. When sunlight passes through the atmosphere, it is scattered in a way that creates a pattern of polarized light, light whose waves vibrate mainly in one direction, arranged in rings around the sun. Humans cannot see this pattern, but many insects can, using specialized areas of their eyes. It lets the beetle find the sun’s direction even when the sun itself is hidden behind a cloud or a tree.
The sun works poorly as a compass when it is almost straight overhead. Studies of South African rollers found that their errors roughly doubled when the sun was very high. A 2019 study showed that around midday, the beetles switch to another cue: the direction of the wind, which they sense with their antennae. When the sun drops lower again, they go back to the sun.
Navigating by moonlight
Some dung beetles roll at night. In 2003, researchers working in South Africa showed that the nocturnal Scarabaeus zambesianus can orient using the faint polarized light pattern around the moon, which is about a million times dimmer than the sunlit pattern. It was the first animal shown to use polarized moonlight for orientation. When the researchers placed a polarizing filter over the beetles and turned it, the beetles turned their path to match.
Steering by the Milky Way
On moonless nights, many beetles still rolled in straight lines, which puzzled researchers. In 2013, a team led by Marie Dacke reported experiments with Scarabaeus satyrus. Outdoors, the beetles rolled straight under a clear starry sky but lost their way under overcast skies, and they also lost their way when fitted with tiny caps that blocked their view of the sky.
The team then tested the beetles in the planetarium in Johannesburg. The beetles oriented just as well when only the Milky Way was projected as under a full starry sky. Their small compound eyes are too coarse to pick out most single stars, but they can see the bright band of the Milky Way. This was the first convincing demonstration of an animal using the Milky Way for orientation, and the first evidence of starlight orientation in an insect.
Do dung beetles use landmarks?
Surprisingly, no. When researchers removed or rearranged nearby trees, bushes and other landmarks, the beetles rolled just as straight as before. When the beetles could not see the sky, they could not keep a straight course at all. The researchers concluded that dung beetles rely on celestial cues so strongly that they ignore the extra precision landmarks could give them, a rare finding among animals with a visual compass.
| Cue | When it is used | Example species studied |
|---|---|---|
| Sun position | By day | Scarabaeus lamarcki, Kheper nigroaeneus |
| Polarized sunlight | By day, also when the sun is hidden | Several day-active rollers |
| Wind direction | Around midday, when the sun is high | South African rollers |
| Polarized moonlight | At night with a moon | Scarabaeus zambesianus |
| Milky Way | On clear, moonless nights | Scarabaeus satyrus |
What about the sacred scarab?
Most navigation research has been done on African species, but the sacred scarab of the Mediterranean is a ball roller of the same genus and also rolls its ball away from dung piles in straight lines. The ancient Egyptians compared its rolling to the god Khepri pushing the sun across the sky, an image that, by coincidence, fits a beetle that steers by the sun so well.
Frequently asked questions
Do dung beetles really use the Milky Way?
Yes, at least one nocturnal African species does. In 2013 researchers showed that Scarabaeus satyrus rolls its ball in straight lines under a starry sky, loses its way when the sky is covered, and orients just as well in a planetarium showing only the Milky Way.
Why do dung beetles climb on top of their ball?
To get their bearings. The beetle climbs up and turns around on the ball, a behavior called the dance, and seems to take a snapshot of the sky. It dances before setting off and again when it loses its ball or gets knocked off course.
Do dung beetles use landmarks?
Apparently not. Experiments in which trees and other landmarks were removed or rearranged had no effect on how straight the beetles rolled, while blocking their view of the sky made them lose their way completely.
How do dung beetles navigate at midday?
When the sun is almost straight overhead, it gives little directional information. In experiments, South African ball rollers then relied more on the direction of the wind, switching back to the sun as it moved lower in the sky.
Where are dung beetles going when they roll a ball?
Nowhere in particular. Unlike bees or ants returning to a nest, a ball-rolling beetle has no fixed destination. It only needs to move away from the dung pile in a straight line until it finds a good place to bury its ball.
Sources and further reading
- Dacke, M. et al., "Insect orientation to polarized moonlight", Nature 424 (2003)
- Dacke, M. et al., "Dung beetles use the Milky Way for orientation", Current Biology 23 (2013)
- Baird, E. et al., "The dung beetle dance: an orientation behaviour?", PLoS ONE 7 (2012)
- Encyclopaedia Britannica, "Dung beetle"
Cite this page
“How Do Dung Beetles Navigate? Steering by Sun and Milky Way.” Animal Atlas, https://animals.bigworldlist.com/questions/how-do-dung-beetles-navigate/.
