As It Happens

Is it a butt or a bug? Newly discovered beetle masquerades as ant's backside

A newly discovered species of beetle gets around by sinking its teeth into the waist of a predatory army ant and disguising itself as the bigger bug's backside.
No, that army ant does not have two rear ends. One of those butts is actually a beetle in disguise. (Daniel Kronauer )

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Meet Nymphister kronaueri, the newly discovered species of beetle that travels long distances by biting the waist of a predatory army ant and disguising itself as the bigger bug's backside. 

"If you look at the ant from the side, you just see that it has two backsides, or two butts if you like, and that's just not normal," Christoph von Beeren, one of the scientists who discovered the beetle, told As It Happens guest host Helen Mann. "It's very difficult to see, because from the top, it just looks like the ant had one butt only."

From above, it's hard to tell this army ant has a beetle attached to its rear. (M. Maruyama)

Von Beeren, an ecologist at Germany's Technische Universitaet Darmstadt, discovered the masters of camouflage while studying army ants with his colleague Daniel Kronauer in the Costa Rican rainforest in the spring of 2014.

The pair were camped out on folding chairs, watching the ants by lamplight, when they noticed their colouring was a bit off.

They collected one into a vial — by literally sucking it through a tube — to get a closer look. 

Christoph von Beeren collects army ants through a sucking tube in the Costa Rican rainforest. (S. Pohl )

First, they noticed the strange double-butt. Then they shook it out of the vial, and the tiny hitchhiker detached.

"Then we realized, 'Oh wow, that was a beetle!' And then we found more and more of them," Von Beeren said. "It was quite exciting."

These brave beetles aren't just latching onto any old insect. Their ride of choice is a species that attacks, dismembers and consumes other insects, spiders and scorpions, and can even kill snakes and birds with its deadly sting.

"These army arts are actually considered a top predator in the tropics, like a jaguar," Von Beeren said.​

Because it wreaks such deadly havoc, more than 300 species, including some beetles, travel in the ant's entourage, most of them feeding off its scraps.

"However, only a few beetles have really gone all in and said: 'Screw it, we're going to literally ride around on the very ants that want to murder us,'" Ainsley Seago, a beetle expert at the Commonwealth Scientific and Industrial Research Organisation, told The Atlantic

It's not clear yet why this butt-beetle tags along with the ants, what it eats or whether their hosts are even aware of them. 

That's why Von Beeren says he's heading back to the rainforest to spend more time with the creatures.

For more on this story, listen to our full interview with Christoph von Beeren.

This close-up image shows the camouflaged beetle chomping into the ant's waist. (Daniel Kronauer)