Parasitic ant queen chemically manipulates workers into killing their mother
By Mindy Weisberger, CNN
(CNN) — Scientists say they have for the first time unlocked how a parasitic ant uses chemical warfare to take over the nest of a different species, by tricking workers into an unlikely assassination.
The deadly scheme unfolds like a Shakespearean drama. In an ant colony, the queen is dying, under attack by her own daughters. Meanwhile, the true enemy — an invader queen from another ant species — waits on the sidelines. Her plan is simple: Infiltrate the nest and use chemical weapons brewed inside her body to deceive the worker ants into mistaking their rightful ruler for an imposter.
In a few hours, the nest’s queen will fall. Once the former matriarch is dead, the invader will assume the role of the colony’s new leader.
Matricide in an ant colony is not unheard of — it typically happens when a colony produces multiple queens or when a solo queen reaches the end of her fertility. But this particular scenario, in which an outsider queen turns workers into her proxy assassins, has never been described in detail before, researchers reported Monday in the journal Current Biology.
In fact, this strategy is yet to be documented in any other animal species, said the study’s senior author Dr. Keizo Takasuka, an assistant professor in the department of biology at the University of Kyushu in Japan.
“Inducement of daughters to kill their biological mother had not been known in biology before this work,” Takasuka told CNN in an email.
The researchers observed this behavior among ants in the Lasius genus, documenting invasions and worker manipulation by queens in the species L. orientalis and L. umbratus.
“Prior studies had reported that, after a new L. umbratus queen invaded a host colony of L. niger, host workers killed their own queen,” Takasuka said. “But the mechanism remained entirely unknown until our study.”
Scent of a worker ant
Ants communicate through smell, which is how they distinguish between nestmates and foes. When researchers previously observed parasitic ant queens near a colony’s foraging trails, they saw that the parasite would snatch up a worker ant and rub it on her body, disguising her scent and allowing her to slip into the nest undetected.
For the new study, coauthors Taku Shimada and Yuji Tanaka — both citizen scientists in Tokyo — each raised an ant colony and introduced parasitic queens. Shimada observed an L. orientalis queen in an L. flavus colony, and Tanaka recorded an L. umbratus queen invading a colony of L. japonicus.
In both experiments, the scientists first co-housed an invading queen with host workers and cocoons “so that she acquired the nestmate odour,” Takasuka said. “This allowed her to gain nestmate recognition and avoid retaliation upon entry.” The scientists then released the queen into the colony.
Both parasite queens followed a similar plan of attack. After disguising their smell, the queens entered the colonies’ feeding areas. Most workers ignored the interloper. Some even fed her mouth-to-mouth.
But the invading queens weren’t there for dinner — they had an assassination to set in motion. After locating the resident queen, the invader sprayed her with abdominal fluid that smelled of formic acid. The scent agitated workers, with some of them turning on their queen immediately and attacking her. Multiple sprays followed, and the attacks became more brutal.
“The host workers eventually mutilated their true mother after four days,” the scientists reported.
All in the family
The death of the true queen was the invader’s cue to start producing hundreds of eggs, attended by her newly adopted “daughters.” Over time, her biological daughters would number in the thousands, usurping the colony until none of the original species remained.
“It’s refreshing to see a very careful observational study that discovers something interesting that we — ‘we’ meaning ant researchers — suspected but had 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 discovery, especially the use of a chemical compound to elicit that behavior by the workers,” said Purcell, who was not involved in the research.
Social insects like ants gather and store resources for the colony to share. That makes them an attractive target for social parasites — species seeking well-stocked nests that they can exploit. Some ant species kidnap the colony’s offspring and enslave them. Others, such as L. orientalis and L. umbratus, set up shop in the colony, where they eliminate the existing queen and take her place.
“There’s all of this amazing diversity,” Purcell told CNN. “What we didn’t know a lot about before this study, is the various ways that socially parasitic queens might go about assassinating the host queen. People had done some observations of direct killing where the infiltrating queen would go and cut off the head of the existing queen. But this is astonishing that they can actually use chemical manipulation to cause the workers to do it.”
Violence within families is often described in fairy tales and myths, with wicked adults — typically desperate parents or jealous stepparents — conspiring to harm or kill children. Rapunzel is imprisoned in a tower; Snow White is hunted 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 her supper.
But while such stories include plenty of violence, the killing of a mother in folklore — let alone children being tricked into matricide — is almost nonexistent, said Dr. Maria Tatar, a professor emerita of folklore and mythology at Harvard University who was not involved in the new study.
In that respect, Takasuka noted, the grim tale of the invading, manipulative ant queens stands out even more.
“Sometimes, phenomena in nature outstrip what we imagine in fiction,” he said.
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