Scientists uncover an ant assassination scheme that helps a parasitic queen rise to power

Scientists claim to have discovered for the first time how a parasitic ant uses chemical warfare to take over the nest of a different species, tricking workers into an unlikely assassination.

The Mortal Plan unfolds like a Shakespearean drama. In an ant colony, the queen dies, attacked by her own daughters. Meanwhile, the real enemy – an invasive queen of another ant species – waits on the sidelines. His plan is simple: infiltrate the nest and use chemical weapons brewed in his body to fool the worker ants into thinking their rightful leader is an imposter.

In a few hours, the queen of the nest will fall. Once the old matriarch is dead, the invader will assume the role of new leader of the colony.

Matricide in an ant colony is not uncommon: it usually occurs when a colony produces multiple queens or when a solo queen reaches the end of her fertility. But this particular scenario, in which a foreign queen turns her workers into proxy assassins, has never been described in detail before, researchers reported Monday in the journal Current Biology.

In fact, this strategy has not yet been documented in any other animal species, said the study’s lead author, Dr. Keizo Takasuka, an assistant professor in the department of biology at Kyushu University in Japan.

“The incentive for girls to kill their biological mothers was not known in biology before this work,” Takasuka told CNN in an email.

Researchers observed this behavior in ants of the genus Lasius, documenting invasions and manipulation of workers by queens of the species L. orientalis and L. umbratus.

“Previous studies had reported that after a new L. umbratus queen invaded a host L. niger colony, the host workers killed their own queen,” Takasuka said. “But the mechanism remained completely unknown until our study.”

Worker Ant Scent

Ants communicate through smell, which is how they distinguish between their nestmates and their enemies. When researchers previously observed parasitic ant queens near a colony’s feeding trails, they found that the parasite would grab a worker ant and rub it on its body, masking its scent and allowing it to slip into the nest undetected.

For the new study, co-authors Taku Shimada and Yuji Tanaka – both citizen scientists in Tokyo – each raised a colony of ants and introduced parasitic queens. Shimada observed an L. orientalis queen in an L. flavus colony and Tanaka recorded an L. umbratus queen invading an L. japonicus colony.

In both experiments, scientists first housed an invasive queen with host workers and cocoons “so that she would acquire the scent of her nest mate,” Takasuka explained. “This allowed him to gain recognition from his nestmates and avoid retaliation upon entry.” The scientists then released the queen into the colony.

Both parasitic queens followed a similar plan of attack. After masking their scent, the queens entered the feeding areas of the colonies. Most workers ignored the intruder. Some even fed her mouth-to-mouth.

But the invading queens weren’t there for dinner: they had an assassination to instigate. After locating the resident queen, the invader doused her with abdominal fluid smelling of formic acid. The smell agitated the workers, with some of them immediately turning on their queen and attacking her. Multiple sprayings followed and the attacks became more brutal.

“The hostesses ended up mutilating their real mother after four days,” the scientists reported.

All in family

The death of the true queen was the signal for the invader to begin producing hundreds of eggs, assisted by her newly adopted “daughters.” Over time, her biological daughters number in the thousands, usurping the colony until none of the original species remain.

“It’s refreshing to see a very careful observational study that discovers something interesting that we – ‘we’ meaning ant researchers – suspected but never confirmed,” said Dr. Jessica Purcell, a professor in the department of entomology at the University of California, Riverside.

“I was really struck by this finding, especially the use of a chemical compound to elicit this behavior in workers,” said Purcell, who was not involved in the research.

Social insects like ants gather and store resources that the colony can share. This makes them an attractive target for social parasites – species looking for well-stocked nests that they can exploit. Some species of ants kidnap the colony’s offspring and enslave them. Others, such as L. orientalis and L. umbratus, move into the colony, where they eliminate the existing queen and take her place.

“There’s all this incredible diversity,” Purcell told CNN. “What we didn’t know much about before this study was the different ways that socially parasitic queens could murder the host queen. People had made observations of direct killings where the infiltrating queen would cut off the head of the existing queen. But it’s amazing that they could actually use chemical manipulation to trick the workers into doing this.”

Violence within families is often depicted in fairy tales and myths, with evil adults – usually desperate parents or jealous in-laws – conspiring to harm or kill children. Rapunzel is imprisoned in a tower; Snow White is chased and then poisoned by an apple; Hansel and Gretel are abandoned in the forest and captured by a witch, who imprisons them and fattens Hansel for his dinner.

But even though such stories include a lot of violence, the killing of a mother in folklore — let alone children being led to matricide — is almost nonexistent, said Dr. Maria Tatar, professor emeritus of folklore and mythology at Harvard University, who was not involved in the new study.

In this regard, Takasuka noted, the dark story of invasive and manipulative ant queens stands out even more.

“Sometimes natural phenomena go beyond what we imagine in fiction,” he said.

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works magazines. She is the author of “Rise of the Zombie Bugs: The Surprising Science of Parasitic Mind-Control.”

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