High atop Borneo's canopied jungles, the ants await any enemy daring enough to invade their colonies.
These are no ordinary ants. They employ a special defense mechanism that isn't so much self-defense as it is species defense.
When attacked, individual ants "explode," releasing their toxic, yellow guts all over their invader while locked in one-on-one combat, according to a new study. It's as if they've initiated their own self-destruct sequence, sacrificing the self to preserve the rest of the colony.
According to researchers from Austria, Thailand and Brunei, who recently discovered 15 new species of a group they are calling Colobopsis cylindrica, or "the exploding ants," minor workers in the species can actively rupture their own body walls.
The ants' peculiar behavior in battle was first described in 1916, but no new species had been cataloged since 1935, according to their study, which was published in the open access journal ZooKeys.
Apart from leading to the ants' imminent death, the defensive "explosion" releases a sticky, toxic liquid from their enlarged glands, in order to either kill or hold off the enemy. The secretion is yellow, with almost the consistency of a curry sauce.
Scientists refer to the kind of self-sacrifice these ants display as "autothysis."
The ants in one particular species, Colobopsis explodens, seemed especially volatile, and had previously gone by the nickname "Yellow Goo," for their brightly-colored toxic secretion.
The scientists deemed members of Colobopsis explodens to be "particularly prone to self-sacrifice when threatened by enemy arthropods, as well as intruding researchers."
For that reason, that particular species will serve as a "model species" for future studies, which the authors say are already in the works. They say they still need to know more about the ants' behavior, chemical profile, microbiology, anatomy and evolution.
While minor workers had the ability to explode, other castes of the species had their own specialties in battle as well. A group known as major workers did not explode as frequently, but used their enlarged, plug-shaped heads to barricade the nesting entrances as intruders advanced on the colony.