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Dung Beetles and Tumblebugs, Subfamily Scarabaeinae

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A pair of dung beetles (Canthon imitator) rolls a ball of dung.

A pair of dung beetles (Canthon imitator) rolls a ball of dung.

Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Where would we be without dung beetles? We’d likely be buried hip deep in poop, that’s where. Dung beetles do the dirty work in our world by breaking down, burying, and consuming animal waste. True dung beetles and tumblebugs belong to the subfamily Scarabaeinae (sometimes called Coprinae).

Description:

The subfamily Scarabaeinae is a large insect group, so there’s quite a bit of variety in the size, color, and shape of dung beetles. Most dung beetles and tumblebugs are black, but a few more flamboyant species come in brilliant shades of green or gold. Dung beetles vary in size from about 5mm to 30mm long. Just below the frons (forehead), the dung beetle’s exoskeleton forms a rounded shield-like structure called a clypeus, which covers the mouthparts. Some male dung beetles possess impressive horns, which they use as weapons to fend off other male competitors.

Even a novice observer can recognize a dung beetle by its behavior. As if by magic, dung beetles appear on fresh dung piles, and quickly begin tearing the patty apart. A single pile of elephant scat attracted 16,000 dung beetles, with 4,000 scatophiles already at work in the first 15 minutes after the poo was deposited on the ground. If you want to see a dung beetle, find yourself a fresh cow patty to observe.

Dung beetles play important roles in the ecosystems in which they live. Gardeners would pay good money to have someone work manure into their soil, but dung beetles provide that service for free. As they roll their balls of poo away, they disperse seeds that passed through the digestive tract of the herbivore and wound up in its scat. Dung beetles and tumblebugs recycle nutrients and help plants thrive. And don’t forget, all those piles of poop attract other, nuisance insects, like filth flies. When dung beetles clean up quickly, they prevent many disease-carrying pests from breeding.

Classification:

Kingdom - Animalia
Phylum - Arthropoda
Class - Insecta
Order - Coleoptera
Family - Scarabaeidae
Subfamily - Scarabaeinae

Diet:

Dung beetles feed primarily on dung, especially of herbivorous mammals, although some beetles in this group feed on carrion, fungi, or even rotting fruit. Dung beetle adults typically derive their nutrition from the liquid component of excrement, and can filter out any solid particles as they ingest it. As the dung dries out, it becomes less palatable to the beetles and they will search for a fresher source of food. Parent dung beetles provision their young with dung balls, so the developing offspring have a ready source of food when they emerge from their eggs. Dung beetle larvae can digest the drier, fiber-rich part of the dung, and use chewing mouthparts to consume it.

Life Cycle:

Like all beetles, dung beetles undergo a complete metamorphosis with four life stages: egg, larva, pupa, and adult.

The mother dung beetle deposits her eggs in dung balls, which the parents skillfully bury or roll into underground tunnels. Each egg is placed in its own chamber, and will hatch within a couple of weeks.

In general, dung beetle larvae will feed for about 3 months, molting through three instars before pupating inside their dung chambers. The adult will emerge from its brood mass in 1-4 weeks, and then dig its way to the soil surface.

Special Behaviors:

The dung beetle makes its living on piles of poop, but that doesn’t mean it’s an easy life. That scat is a veritable free-for-all of dung beetles trying to grab the nicest hunk and run. A sneaky dung beetle might lie in wait for a more ambitious beetle to do the work of rolling a nice, neat dung ball, and then dash in and steal it. It’s in the dung beetle’s best interest to retreat quickly with its poo prize, and that means it needs to roll the ball in a straight path. Should the beetle inadvertently push its dung ball in a curve, it risks winding up back in the melee, where a beetle bully can cause trouble.

It’s no easy task to roll a ball of poo in a straight line, especially when you do so by pushing it from behind with your back legs, and your head down. Researchers studying dung beetles in Africa have recently shown that the beetles look to the heavens for navigational clues. The sun, moon, and even the gradual gradient of light that we call the Milky Way can help the dung beetle maintain a straight line. And each time a dung beetle encounters an obstacle – a rock, a depression in the soil, or perhaps a clump of grass – it climbs atop its dung ball, and does a little orientation dance until it figures out which way to go.

Range and Distribution:

Dung beetles are both abundant and diverse, with roughly 6,000 species in over 250 genera known so far. Dung beetles live on every continent except Antarctica.

Sources:

  • Ecology and Evolution of Dung Beetles, edited by Leigh W. Simmons and T. James Ridsdill-Smith.
  • Borror and DeLong’s Introduction to the Study of Insects, 7th edition, by Charles A. Triplehorn and Norman F. Johnson.
  • Encyclopedia of Insects, 2nd edition, edited by Vincent H. Resh and Ring T. Carde.
  • Insects: Their Natural History and Diversity, by Stephen A. Marshall.
  • Scarabaeinae Overview, Generic Guide to New World Scarab Beetles website. Accessed May 8, 2013.
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