This parasitic ant tricks workers into committing matricide

Overtaking a throne sometimes takes a touch of matricide. 

Some newly mated ant queens sneak into other ant colonies and spray their queens with a liquid that sends workers into a murderous frenzy, researchers report November 17 in Current Biology. After the workers do the parasitic queen’s dirty work, she can ascend the throne and begin laying her own eggs.

“This is, to our knowledge, the first case where a third party benefits from matricide,” says Keizo Takasuka, a behavioral ecologist and entomologist at Kyushu University in Fukuoka, Japan. 

Matricide is exceedingly rare in nature, probably in part because motherly love is a strong force that helps keep offspring alive. The few known examples, found in invertebrates, include mothers sacrificing their body so their young can eat or workers killing queens to push the colony to produce more males. 

But newly mated Lasius orientalis and L. umbratus queens — relatives of the black garden ant (L. niger) — can push L. flavus and L. japonicus worker ants to turn on their own mother. Historical records from the early 1900s reported that some Lasius workers commit matricide. What instigated the ants’ betrayal, however, was unknown. 

In tabletop colonies constructed out of small containers connected to a tiny feeding station, Takasuka and colleagues watched as L. orientalis and L. umbratus queens executed a coup. Each parasitic queen first spent time with workers to steal their smell, duping them into thinking that she was a member of the colony. Then she made her way close to the current queen, drenching her in a spray that sparked a revolution among the workers, who attacked until the queen was dead. 

The spray is probably formic acid, a chemical irritant that some ants use as a defense, the team says. Tests with synthetic formic acid could help confirm whether that chemical alone incites matricide, Takasuka says, or if another chemical is also involved. 

It can take a few sprays to get the job done. One L. umbratus queen sprayed a L. japonicus queen just twice before the workers ultimately killed their mother in half a day. But a L. orientalis queen sprayed her victim 16 times in 20 hours. The workers attacked the L. flavus queen until she died four days later and they dismembered her. 

Other parasitic ants typically take over nests by directly killing another queen, says Christine Johnson, a behavioral ecologist at the American Museum of Natural History in New York City, who wasn’t involved with the work. Tricking worker ants into doing the dirty work may be an evolved tactic to steal the throne with a lower risk of injury or death. 

Still, removing the old queen doesn’t guarantee a successful takeover for the new queen. “She can be accepted,” Johnson says. “But it doesn’t necessarily mean they’re going to adopt her young.”