Ants attack their nestmates because pollution changes their smell

Forager ants attack nestmates whose odor they do not recognize

JorgeOrtiz_1976/Shutterstock

Common air pollutants such as ozone and nitrous oxide can change the way ants smell and cause their nestmates to attack them as if they were intruders.

Ants recognize their mates by smell, and when they encounter an ant whose smell they do not recognize, they react aggressively, biting and sometimes killing the intruder. But ozone, a greenhouse gas produced by cars and industrial activities, can disrupt the structure of alkenes, the chemicals that make up some of the colony’s specific scents.

Markus Knaden from the Max Planck Institute for Chemical Ecology in Jena, Germany, and his colleagues knew from previous work that ozone-induced changes in alkenes could disrupt the way insects communicate with each other. They witnessed fruit flies mating with the wrong species and pollinators such as hawks lose interest in flowers if their scent were altered by ozone.

To test the impact on ants, Knaden and his colleagues created artificial colonies of six species of ants. They removed one individual ant from each and placed it in a glass chamber filled with different concentrations of ozone, some of which matched the levels measured in Jena in the summer. When they returned the ant, the others attacked him.

“I have to say, I didn’t expect that,” says Knaden. “Because knowing that alkenes are such a small part. [of the ants’ scent]We knew that whatever we did to the ozone would only change maybe 2 or 5 percent of the mixture.”

In the wild, this kind of behavior could make the colony less efficient, he says, even if the ants aren’t killed, but designing experiments to capture those effects will be complicated.

Daniel Kronauer of The Rockefeller University in New York, who was not involved in the study, says that alkenes are very important for recognizing a nest mate, so he was not shocked by the aggressive responses.

Alkenes are involved in other ant behaviors such as trail tracking and larval-adult communication. The study found that when exposed to ozone, adult clonal raider ants (Ooceraea biroi) can neglect their larvae, so these ozone-induced changes have the potential to disrupt multiple aspects of ant life—as well as the broader ecosystem.

“If you removed ants from most terrestrial ecosystems, they would probably collapse,” says Kronauer. This is because ants have essential ecological roles. They disperse seeds, move soil and have mutually beneficial relationships with many organisms.

Insect populations are in sharp decline worldwide, and this study adds to a growing body of research pointing to air pollutants as one factor in the decline. Knaden says that while the levels of ozone pollution we’re experiencing may not yet be harmful to humans, “we should just know that what we’re doing has additional costs that we may not have considered before.”