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New 'exploding ant' species also blocks invaders with its massive head

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By Belinder Smith Science Reporter

Anyone who's accidentally stood on an ant nest will know just how good they are at defending their home, but a new "exploding ant" species takes it to the next level. 

When confronted by an enemy insect, these tree-dwellers latch onto their foe, tear open their own body wall and release yellow toxic goo onto their rival, slowing or killing it.

And while this "explosion" doesn't exactly blow them to bits, it also spells the end for the defending ant, said Alice Laciny, a PhD student at the Natural History Museum in Vienna who described the recently discovered species, dubbed Colobopsis explodens, in the journal ZooKeys today..

"It's a bit like the mechanism of when a bee stings," she said.

Such "suicidal defence" is only common in social insects, such as ants, bees and termites, she added.

"An ant colony shouldn't be treated as a family of individuals, but really like a super organism, and each ant acts more like a cell in a body and it has its own role to play."

Active and passive resistance

Found in Borneo, only the minor workers of the newly described ant species are capable of self-exploding.

Their body is filled with long glands, which hold the sticky goo. When they contract their backside hard enough, the liquid oozes out, like toothpaste squeezed from a tube.

But many ant species are polymorphic, according to Alan Andersen, an ant ecologist at Charles Darwin University.

"This means the workers come in different shapes and sizes."

C. explodens is no exception. Where minor workers look like a pretty normal ant, the beefier major workers have a relatively gigantic head.

"The entrance to their nest is a small hole, pretty much exactly the same diameter as the head of the major workers," Ms Laciny said.

"So they actually just stick their head in the hole and plug it up, so nothing can get inside.

"Where the minor workers are kamikaze, the major workers are more like passive resistance."

While Australia doesn't host any exploding ants, we do have a few species with so-called "plug head" members, Professor Andersen said.

A coastal species — Camponotus anderseni, named after Professor Andersen — lives in the twigs of mangroves in the Top End.

"Their nests are inundated by the tides every tidal cycle, so the nest of these ants is underwater for large periods of time every day."

When the tide comes in, plug-head ants wander up to the entrances and lodge their head in to create a water-tight seal.

"So these ants plug the nest entrances, not to keep enemies out, but to keep water out."

It's such an effective way to keep stuff out of the nest — whether it be invading insects or the ocean — that plugging behaviour has independently evolved over and over again.

A slightly different plugging action is carried out by some ant species in the US, Professor Andersen said.

These drop stones in the entrances of a more-dominant ant species, effectively trapping them inside until they can bust their way out.

More bizarre but brilliant behaviours

Another group of ants with an incredible defence mechanism found in Australia is the trap-jaw ants, said James Cook University ant ecologist Lori Lach.

These sport a pair of long, straight mandibles that are usually held open until tiny trigger hairs on the inside of the mandibles are tripped and the jaw snaps shut.

"They have the fastest moving body parts of any animal in the world," Dr Lach said. 

"It's helpful to capture prey, but it's also been documented that if they're threatened, they snap them against the ground.

"The force propels them to flip away. They essentially do backflips away."

Leafcutter ants must contend with parasitic flies, which lay their eggs on ant heads, Dr Lach said.Along with plug-heads, exploders and backflippers, some ants have also found ways to avoid threats from above.

"When the egg hatches, the larvae burrow into the ant head and eat it from the inside out."

So when foraging leafcutters head out above ground, they need a bodyguard.

This comes in the form of a tiny worker ant which sits atop the leaf, Dr Lach said.

"They're there to shoo away the flies that might come and lay their eggs on the heads of the larger ants.

"People think ants are pests, if they notice them at all. But they're so fascinating. They've figured out so much."


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