A sneaky, stealthy parasite queen can turn an ant colony against itself. Newly-mated queens of two parasitic ant species have been found to sneak into an ant colony, creep towards the resident ant queen, and spray a chemical to trigger matricide, i.e., tricking ants into slaughtering their own mother so she can take over the colony.
Matricide is a rare phenomenon in nature, seldom observed, especially among animals that receive substantial benefits from maternal care. While some insects may kill their queen under certain circumstances, these usually serve the evolutionary interests of the workers. But, in this newly discovered case, the queen elimination in Lasius flavus and Lasius japonicus species arises in a parasitic context, triggered by the invading ant queens from other species – Lasius orientalis or Lasius umbratus.
“I first learned of induced matricide – and I was so stunned that I was at a loss for words for a while,” says the study lead author, Keizo Takasuka, in an email to New Atlas.
In their new study, Takasuka and her colleagues describe an intriguing form of social parasitism in the journal Current Biology. The researchers examined the two parasitic ants, L. orientalis and L. umbratus. After mating, these queen ants started their search for a host colony, such as L. flavus and L. japonicus, and acquired the host odor through direct physical contact with a host worker.
After soaking up the host colony’s scent, the invading queen wanders unnoticed through the nest like an undercover spy to locate the resident queen. On getting closer to the resident queen, she bends her metasoma (abdomen) and sprays an unidentified fluid at the host queen. Researchers hypothesize the sprayed fluid is formic acid.
“Formic acid is a hallmark secretion of the subfamily Formicinae – the group to which Lasius belongs. Given that formicine ants actively use formic acid for various purposes, it is a parsimonious hypothesis that the sprayed fluid here is also formic acid,” Takasuka tells us.
Immediately after the spray, the host workers become agitated by the odor of the formic acid and begin attacking their own mother queen. Takasuka says that the fluid effectively turns the host queen into a perceived menace, a high-priority enemy, rather than merely raising general aggression.
The parasitic ant then repeatedly sprays the host queen every few hours. The worker ant attacks on their queen get more intense with each spray. The study recorded almost 15 sprays from the parasitic queen before the host workers killed and dismantled their mother.
Within 10 days of this matricide, the rival queen starts laying eggs and is accepted as a new queen of the colony.
“I see it just as a fascinating, brutal survival strategy,” Takasuka told us.
Takasuka says that temporary social parasitism has evolved twice within Lasius, and induced matricide appears to have evolved independently in those lineages as well. This suggests that once a parasite possesses a chemical or spraying mechanism that can trick the host workers into perceiving their own queen as an enemy, indirect queen-killing can achieve the goal of colony takeover at a lower risk than direct attack. This provides favorable conditions that preference the evolution of induced matricide.
The study was published in the journal Current Biology.
