Parasitic ant tricks workers into killing their queen, then usurps her

A type of parasitic ant takes over the colonies of a related species by inciting the workers to kill their queen, then taking her place.

Around 230 species of ants are considered parasites – they lay their eggs in other species’ colonies or steal their larvae and pupae. Some kill the host queens before laying their own eggs and convincing the workers to serve them instead.

Keizo Takasuka at Kyushu University in Fukuoka, Japan, and his colleagues noticed that, when a queen of the parasitic species Lasius orientalis was accidentally introduced into the nest of its relative, Lasius flavus, the flavus workers would then kill their own queen – their mother.

Many parasitic queens are killed by workers once they are discovered, but some get through the colony’s defences, apparently by cloaking themselves in the scent of the colony.

To observe how the parasitic queens succeeded, the researchers assisted them by cloaking the female intruders with the scent of the worker ants before introducing them to the colony.

“It’s reminiscent of the zombie television series, The Walking Dead, where characters smear themselves with walker blood to pass through a horde — it involves camouflage that often fails, and those who are exposed are killed brutally,” says Takasuka.

Once the parasite gets into the colony, she sprays the rival queen with a chemical, thought to be formic acid, from an orifice at the tip of her abdomen.

The workers interpret this chemical as a danger to the colony and immediately attack their queen once they smell it. However, the process is slow, taking multiple sprays and many attacks from her workers before the queen is eventually killed. Then the parasitic queen can lay her own eggs, which are tended to by the workers.

“If the parasitism succeeds, it allows the new queen to pass through the vulnerable founding phase far more safely than founding a colony alone,” says Takasuka. “I suspect this strategy may be more widespread than we currently appreciate.”

Chris Reid at Macquarie University in Sydney, Australia, says the complex behaviours of ants are difficult to observe because they occur in the privacy of the underground nest.

“This kind of natural history detective work is vital for improving our understanding of these super important insects,” says Reid. “Further study could even lead to new ways to target the queens of invasive ant species, which are one of the biggest challenges facing ecosystems worldwide.”