Minor worker of Colobopsis explodens with posterior body raised in a defensive pose. (Alexey Kopchinskiy/Pensoft Publishers)

It’s not easy being a bug, especially one as small as an ant. The list of potential predators is lengthy for the diminutive creatures, so it’s no wonder they’ve developed an arsenal of defense mechanisms including painful bites, stings and overpowering enemies by sheer numbers.

But one newly discovered ant species goes above and beyond when it senses danger. It explodes — killing itself — and coats adversaries in a toxic yellow goo, the ultimate act of self-sacrifice to protect its colony.

These valiant ants are the newest addition to the species group Colobopsis cylindrica, more colloquially known as “the exploding ants,” according to a detailed survey of the insects published Thursday in ZooKeys, a peer-reviewed open access scientific journal. Found in the jungles of Southeast Asia, the tree-dwelling ants were called “Yellow Goo” before researchers aptly named them Colobopsis explodens, Alice Laciny, the article’s lead author, told The Washington Post. They are the first new species of exploding ant to be discovered since 1935, Laciny said.

The small reddish-brown ants look like any other ant. But their bodies are full of glandular sacs containing a deadly fluid, said Laciny, an entomologist at the Natural History Museum in Vienna, as well as a PhD student at the University of Vienna.

In the ant hierarchy, they are minor workers, a colony’s expendables. But there’s nothing cinematic about the ants’ final act of heroism. “The explosion is not as dramatic as people think it is,” Laciny said.

Rather, the ants will bite down on the enemy, angle their backsides close and contract their muscles so hard their skin splits open, releasing the goo, Laciny said. The sticky substance, which oddly has a “spice-like, curry-like” scent, then either kills the intruder or hinders its attack, she said.


Exploding behavior of the ant in an experimental setting with a weaver ant. (Alexey Kopchinskiy/Pensoft Publishers)

If enemies survive the first line of defense, they will come face to face with the colony’s major workers and their enlarged, plug-shaped heads, researchers wrote. Known as “doorkeepers,” these ants barricade the nest’s entrance, providing a second line of defense.

Although exploding ants were first observed by scientists more than 100 years ago, not much was known about them, including how many different kinds existed.

In 2014, Laciny and a group of researchers — composed of entomologists, botanists, microbiologists and chemists from Austria, Thailand and Brunei — set out to document the exploding ants, according to a summary by the journal’s publisher. The scientists determined there are at least 15 different kinds of these self-sacrificing insects, including this one.

Despite all the research that has been done, Laciny said there is still much more to be learned about the exploding ants, and Colobopsis explodens is expected to be at the center of it all.

The newly identified ant species was selected as the group’s model species, after the scientists deemed it to be “particularly prone to self-sacrifice when threatened by enemy arthropods, as well as intruding researchers,” the summary said. In that role, the ant will serve as a reference point for future research about exploding ants, Laciny said.

“They’re really nice to watch in their exploding behavior,” she said. “They do it quite readily. We have some species who don’t really like to explode as much.”

However, Laciny said these ants will not explode for any old reason. They do it only in response to attack, a  “form of active self-sacrifice” that kills them. The ants need to “really be provoked,” she said.

Minor workers are not capable of reproducing, which is why they can be sacrificed. Still, they play a crucial role in the long-term survival of the species. Laciny said their dramatic death helps ensure a colony lives on, so that others may reproduce. “Their way of protecting their genes is protecting their sisters.”

“Imagine a single ant is like a cell in a human body,” she said. “The exploding workers work as immune cells. They sacrifice their lives to hold off danger.”

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