Invading parasitic ant queens trick workers in various colonies into killing and dismembering their own mothers, allowing the invaders to intervene and usurp the throne, according to a new study.
“The queen’s odor is erased by formic acid, instantly turning her most urgent protection into a deadly threat. This is nothing short of a nightmare for the host queen and the workers alike,” study lead author Keizo Takasuka, a biologist at Kyushu University in Japan, told LiveScience in an email.
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Some species of ants, such as Lasius orientalis and Lasius umbratus, act as social parasites. Rather than starting their own colony from scratch, the queen bees of these species invade and occupy colonies of other species, such as Lasius flavus and Lasius japonicus, and serve their workers in their place.
Scientists already knew that these invasive queens used stolen scents to disguise themselves as members of the colony. This works because ants have limited vision and their nests are dark, so workers rely heavily on smell for recognition and decision-making.
But they still didn’t know how the intruders convinced the workers’ daughters to kill their mothers. To find out, Takasuga and his colleagues studied the behavior of ants in the lab. The findings were published on Monday (November 17) in the journal Current Biology.
Takasuga said they first placed the host workers and cocoons on the invading queen to ensure they got the right scent.
This scent acquisition mimics what happens in the wild, Daniel Cronauer of New York’s Rockefeller University, who was not involved in the study, told Live Science. “These queens are sometimes found outside of their host species’ colonies, but they can acquire a kind of transparency because they bite host workers and groom themselves with host worker chemicals,” he said.
Next, the researchers introduced L. orientalis queens into L. flavus nests and L. umbratus queens into L. japonicus nests.
Most of the invading queens were accepted by the workers and proceeded towards the host queen.
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Each parasitic queen squirted peritoneal fluid at the host queen and retreated as soon as the excited workers launched an attack toward their own queen. If the host queen survived the onslaught, the parasitic queen would return to spray her again, but eventually the host queen would be killed and dismembered by her own daughters.
When threatened, ants can spray formic acid, which has a sharp vinegar-like odor. Takasuga believes that the ants are spraying the queen.
“When ants are attacked, they often spray the intruder with formic acid as a way to alert other ants in the colony,” Cronauer said. “So it makes a lot of sense that this would be reused by the parasitic queen. Basically, by spraying formic acid, she’s telling them that the queen is an intruder, which triggers the attack.”
Once the situation calms down, the parasitic queen begins to lay her own eggs, and worker ants take care of the queen and her offspring. At this point, workers are constantly crawling over the queen, Cronauer said, and the queen blends into the scent of the entire colony. “So the queen parasite doesn’t have to keep killing or biting the worker bees.”
Eventually, the old workers become extinct and all the descendants of the parasitic queen become her descendants.
In some other parasitic ants, the invading queen kills the incumbent ant herself. Matricide, or the killing of the mother by the offspring, is rare in nature, and when it does occur, it tends to be to the benefit of the species, as when mothers of the earwig (Anetula harmandi) offer themselves as food for their larvae, or when the queen bee is killed to increase diversity within a colony.
But in the case of these ants, only the parasitic species benefit. “From a social parasite perspective, this is a selfish and manipulative act. And what the resident workers are doing is very stupid and maladaptive,” Cronauer said.
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