QuestionSacred scarab
Why Do Dung Beetles Roll Dung Balls? Food and Nurseries
Dung beetles roll dung into balls so they can carry a share of food away from the crowded, competitive dung pile and bury it somewhere safe. Some balls are eaten by the beetle itself. Others become brood balls: underground nurseries in which a female lays an egg, so her larva grows up surrounded by food.
Contents
Why roll the dung away?
Fresh dung is a rich but short-lived resource. Within minutes of an animal leaving a pile, dung beetles start arriving by smell, and at large piles, such as elephant dung in Africa, researchers have counted thousands of beetles arriving at a single heap. The pile also dries out in sun and wind, so the food does not last long.
Competition at the pile is fierce, and beetles regularly try to steal each other’s work. Rolling solves both problems at once. A beetle that shapes a portion into a ball can move it several meters away, out of reach of rivals, and bury it in soil where it stays moist. That is why rollers set off in a straight line: a straight path takes them away from the crowd fastest and avoids circling back into it. How they keep that straight line is explained in how dung beetles navigate.
Rollers, tunnelers and dwellers
Not every dung beetle rolls. Ecologists divide dung beetles into three groups by how they handle dung:
| Group | What they do | Examples |
|---|---|---|
| Rollers | Shape dung into balls and roll them away before burying them | Scarabaeus, Kheper, Gymnopleurus |
| Tunnelers | Dig burrows directly under the pile and pull dung down into them | Onthophagus, Copris, many dor beetles |
| Dwellers | Live, feed and lay eggs inside the dung pat itself | Many small Aphodius beetles |
Rollers are the most famous, but tunnelers often move more dung in total. Many beetles of all three types are found at the same pile, sharing it out in different ways.
Food balls and brood balls
A feeding ball is a packed lunch. The beetle rolls it to a suitable spot, digs a chamber, pulls the ball down and eats it underground over several days before going back to look for more dung.
A brood ball is a nursery. Females choose finer dung for it, bury it deeper and shape it carefully. In the sacred scarab of the Mediterranean, the female molds the buried dung into a pear shape and lays a single egg in a small chamber in the narrow end. The larva hatches into a complete food supply, eats the dung from the inside, pupates in the hardened shell and finally digs out as an adult. This care means each female raises only a few young, but each has a good chance of surviving.
In some rollers, such as the large copper dung beetle of southern Africa, a male and a female travel together. The male pushes the ball, while the female clings to it or follows behind. When they find soft soil, they bury the ball, mate underground and prepare a brood ball together.
How do dung beetles roll their balls?
Most rollers push the ball backward. The beetle stands on its front legs with its head down and grips the ball with its long middle and hind legs, then walks backward, pushing with its back legs. If the ball rolls away or hits an obstacle, the beetle climbs on top, turns around to check its bearings, and sets off again in the same direction.
Large ball-rolling beetles can move balls that weigh many times their own body weight. Strength records are often quoted for dung beetles, but they come from different kinds of tests: the most famous figure, about 1,141 times its own body weight, is the force a male Onthophagus taurus could exert inside its burrow to resist being pulled out. That beetle is a tunneler, so the record says nothing about how heavy a ball a roller can push.
How much dung do dung beetles clear?
A great deal. Some species can bury many times their own weight of dung in a single night, and the dung of one large animal can feed huge numbers of beetles. By burying dung, beetles:
- return nitrogen and other nutrients to the soil, where plant roots can use them
- loosen and aerate the soil and help water soak in
- remove dung where pest flies and livestock parasites would breed
- bury seeds found in dung, helping some plants spread
Researchers have estimated that dung beetles save the US cattle industry about 380 million dollars a year by burying livestock dung on pastures.
Australia’s dung beetle project
Australia shows what happens when dung is not recycled. Native Australian dung beetles evolved with marsupial droppings and largely ignore the large, wet pats of cattle, which were introduced by European settlers. Cow pats lay on pastures for months, smothering grass and breeding flies.
From 1965 to 1985, the national research agency CSIRO ran the Australian Dung Beetle Project, introducing dung beetles from Africa and Europe. Twenty-three species became established. They improved pasture quality and helped reduce the numbers of pest bush flies in many areas.
Myths and facts about ball-rolling
Myth: dung beetles call others to help them. Fabre’s 19th-century observations showed that the “helpers” were usually would-be thieves.
Myth: all dung beetles are ball-rollers. Most species are tunnelers or dwellers.
Fact: the ancient Egyptians noticed ball-rolling. They linked the beetle pushing its ball with the god Khepri rolling the sun across the sky. Read more in why the scarab was sacred in ancient Egypt.
Frequently asked questions
Do all dung beetles roll balls?
No. Only the group called rollers shapes dung into balls and moves it. Tunnelers bury dung directly beneath the pile, and dwellers simply live and breed inside the dung, so most dung beetle species never roll a ball at all.
What is inside a dung beetle's ball?
A feeding ball is simply dung that the beetle will eat underground. A brood ball also contains a single egg, laid in a small chamber inside, and the larva that hatches eats the dung around it until it becomes an adult.
Why does a female ride on the ball?
In some species a male and a female travel together. The male usually pushes while the female clings to the ball or follows, and the pair bury the ball, mate underground and prepare a brood ball for their young.
How big is a dung beetle's ball?
It varies with the species and the dung. Small rollers make balls the size of a pea, while large African species can roll balls bigger than a tennis ball, often many times the beetle's own weight.
Do dung beetles help each other roll balls?
Usually not. A second beetle that seems to be helping is often a thief waiting for a chance to take the ball, a point the French naturalist Jean-Henri Fabre showed in the 19th century. Genuine teamwork is mostly between a male and female pair.
Why are dung beetles important?
By burying dung they recycle nutrients into the soil, loosen and aerate it, and remove breeding places for flies and livestock parasites. In the United States alone, their work on pasture dung has been valued at about 380 million dollars a year.
Sources and further reading
- Hanski, I. and Cambefort, Y. (eds.), Dung Beetle Ecology (Princeton University Press, 1991)
- Encyclopaedia Britannica, "Dung beetle"
- Nichols, E. et al., "Ecological functions and ecosystem services provided by Scarabaeinae dung beetles", Biological Conservation 141 (2008)
- Losey, J. E. and Vaughan, M., "The economic value of ecological services provided by insects", BioScience 56 (2006)
Cite this page
“Why Do Dung Beetles Roll Dung Balls? Food and Nurseries.” Animal Atlas, https://animals.bigworldlist.com/questions/why-do-dung-beetles-roll-balls/.
