These Ants Explode, but Their Nests Live to See Another Day

Outside the kitchen door at the Kuala Belalong Field Studies Center in Brunei, on a number of trees near the balcony, there is a nest of very special ants.

They explode.

This colony was studied in depth by scientists who, last week in the journal ZooKeys, published an in-depth description of the newly named species, called Colobopsis explodens, including a portion of their genome sequence.

Workers of C. explodens have a distinctive, rather foul talent. When their nest is invaded, they rupture their own abdomens, releasing a sticky, bright yellow fluid laced with toxins on their attackers. Similar to honey bees that die after stinging, the exploded ants do not survive, but their sacrifice can help save the colony.

Exploding ants have been known to science for more than 200 years, and the special ability for which they are named was first documented in 1916. But since 1935, no new species from the group had been officially named and described.

To do this, ideally one needs to collect members of all the different castes in the colony, from worker to queen, write a detailed description of their appearance, and give the species a Latin name, among other things, said Alice Laciny, a graduate student at the Natural History Museum Vienna who is an author of the new paper.

“We knew they existed, and we did experiments on them,” she said, “but it wasn’t described as an official species yet.”

Laciny is a member of an eclectic group of researchers who are united by their fascination with these insects and who describe in the new paper how C. explodens live and spectacularly die.

At 6 a.m., the ants come out of their nest and forage for food until about 6 p.m., the researchers found, although it is not exactly clear yet what they eat. A small squad of workers often stands at the entrances of the colony and touches every ant that comes in or out, apparently monitoring the movements of their sisters. The researchers also introduced a weaver ant, a natural predator of exploding ants, to observe the workers’ explosive response.

“Their whole body is filled up with these glandular sacs that are full of sticky fluid,” said Laciny.

When a predator touches a worker, the worker will often rupture, tangling the predator in a gluey mess and eventually poisoning it. This strategy of voluntary self-sacrifice makes evolutionary sense because the ants of the colony are all closely related, and the workers are sterile.

“Their way of taking care of their own genes is to sacrifice themselves so the rest of the colony can survive,” Laciny said.

Laciny is not sure that she will ever see the nest by the kitchen door again. The project’s funding is ending soon, and for now the group is working to understand what the ants’ goo is made of and publishing papers based on their observations, as well as describing several more new species of exploding ants.

“Now I just have them dead and pinned and glued to little paper cards at the museum,” Laciny said of her subjects. “And of course, I like them better when they are alive.”