More than you ever wanted to know about dung beetles

Thanks to Sir David Attenborough and Ze Frank, much of the world is familiar with the roly-poly dung beetle, the persistent little creature that spends its life pushing boulders of poop around. And even if you don’t have a lot of respect for bugs that dine on faecal matter, who can deny the sheer awesomeness of the way the beetles use the haze of the Milky Way to navigate at night?

What’s not so beautiful is the paper I recently stumbled across in an Indian medical journal detailing 18 cases of something called 'scarabiasis', which is what they call it when dung beetles force their way inside a child’s rectum and set up shop. According to the article, the beetles can even be seen flying away upon defecation.

Now, because that’s one of the craziest damn things I’ve heard in a long time, I had to find out if it was even remotely possible. (Remember, kids, just because you read something on the internet doesn’t mean it’s true.) There are, of course, all sorts of creepy crawlies that colonise the human body, from botflies to tapeworms, but the idea that a beetle accustomed to living in a dung heap could come and go from the human rectum as it pleased smelled a little like, well, you know.

To get some answers, I called up Brett C. Ratcliffe, curator and professor at the University of Nebraska-Lincoln. Among entomologists, Ratcliffe’s lab is known as Scarab Central, and it boasts the fourth-largest scarab beetle collection in the world – behind London, Berlin and Paris. All dung beetles belong to Scarabaeoidea, the superfamily of beetles Ratcliffe has been studying for the last 45 years, so if any of them are capable of conquering the human digestive tract, he should be hip to it.

“Unless I saw actual, verified case reports, I would doubt this,” said Ratcliffe.

For one, beetles require oxygen to survive – just like you and me – and that’s not really part of our digestive tract’s anatomy. As to whether the children may have ingested faecal matter infested with beetle larvae, which then somehow survived long enough to mature into adults, Ratcliffe says flatly, “No, no, no. No way.”

“The idea that a beetle accustomed to living in a dung heap could come and go from the human rectum as it pleased smelled a little like, well, you know.”

Instead, Ratcliffe suspects the beetles were crawling up to the naked children while they slept and, ahem, doing what dung beetles normally do – trying to gather faeces for food. In fact, in his field research, Ratcliffe has observed other species of scarabs getting up close and personal with the source.

“There are a number of dung beetles that adhere very closely to the anus of monkeys from South America,” Ratcliffe said. “In tropical rainforest ecosystems, dung is a very valuable and limited resource, so rather than waiting for it to fall to the ground where randomly searching dung beetles can then find it, these beetles are actually waiting by the anus of the monkey. They grab it as it falls out and actually fall to earth with it.”

Yes, this means scientists spent weeks in the Peruvian rainforest watching brown titi monkeys and bald-faced saki monkeys poop. As you might imagine, many fantastic details emerged. Lead author Jennifer Jacobs writes that, from afar, the dung beetles glistened on the monkeys’ genitals as if they were jewels or shiny droplets of water. (Ines Nole and Susanne Palminteri were co-authors on that excellently named paper, "First come, first serve".)

Here's photographic proof ... the dung beetles really did glisten. Images: Job Aben, courtesy of Jennifer Jacobs.

Later in the study, a plummeting piece of dung fell directly into a research assistant’s pocket. I mean, honestly.

Perhaps most interesting of all though is the fact that the monkeys didn’t seem to have much of a problem with relatively large beetles hanging around their butts all day. The team observed a juvenile twice pluck a beetle off and fling it into the air – like a child might a booger – but other than that, the monkeys just let the hitchhikers be. (The beetle flew right back to the juvenile’s butt, by the way.)

And monkeys aren’t the only ones. Some of Ratcliffe’s other research shows three-toed sloths host a number of dung-loving scarabs. The sloths climb down from the canopy once a week to defecate and bury their dung (more on that here), at which point the beetles hop off the ride. And another genus of dung beetle, Zonocopris, has been found hiding out in the shells of giant South American land snails. Across the ocean in Australia, where dung is quick to dry out, six species of beetles in the genus Onthophagus wield claws specially adapted to better grasp mammal fur and have also been observed dropping off marsupials when they make.

So, are the reports of scarabiasis really just a handful of confused dung beetles attracted to a familiar scent? Well, I can at least tell you that there’s ample evidence that dung beetles of numerous species are attracted to human waste. Part of Ratcliffe’s monkey study included baiting traps with human faeces to see if free-ranging dung beetles would find it. (They did.) Other studies have concluded that dung beetles have dung preferences. And some species, like those in the genus Phanaeus, actually show a “decided preference for human dung”.

I know, all of this is pretty gross. And you’ve been a good sport, sitting through all that stuff about monkey butts and dung flavours and those poor little kids in India. So allow me to leave you on a finer note.

There’s a beetle in the genus mentioned above that doesn’t look like it belongs anywhere near a pile of dung. Some call it the rainbow scarab, but technically it goes by Phanaeus vindex – and it might be the prettiest beetle at the ball.

Males have shiny green and purple armour and wield large, impressive horns, which they use to battle other males for mates like tiny, electric Kool-Aid rhinoceroses. These little buggers may look exotic, but they’re actually found across the eastern United States, from Texas to Florida and on up into Massachusetts.

Instead of rolling balls away from a dung pile like the beetles you’ve seen on TV, P. vindex burrows down beneath it. They then drag balls of tasty dung down the hole behind them, lay an egg inside and seal the tunnel back up.

P. vindex and other tunnelling dung beetles play an enormous role in the ecosystem, helping to break down animal waste and draw it below ground where it fertilises the soil. As Ratcliffe put it, without dung beetles, you’d basically have to sidestep poop everywhere you went.

And if iridescent beauty and ecological utility aren’t enough to win you over to Team Dung Beetle, then perhaps you can take comfort in this fact: some animals have learned to use the beetles’ penchant for poo against them.

Scientists have observed burrowing owls (Athene cunicularia) carrying pieces of mammal dung back to the entrance of their lairs. The smell of the dung acts like a pie cooling on a windowsill and draws in dozens of different species. The owls then simply sit on their front stoop and nibble whatever looks tasty. The lure is so effective, owls that go fishing with mammal dung eat ten times as many beetles as owls that don’t.

Poor, poor little dung beetles.

Top header image: Geoff Gallice, Flickr