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Ant supercolonies invading cities, study finds

It’s not only humans that flourish in large settlements. Some ants find urban life so accommodating that their populations explode and they form supercolonies in cities.

“One of the most common house ant species might have been built for living in some of the smallest spaces in a forest, but the ants have found ways to take advantage of the comforts of city living,” Purdue University said in a statement today.


Grzegorz Buczkowski discovered odorous house ants living in supercolonies, creating complex networks entomologists have never seen with the species before now.

Purdue Agricultural Communication photo/Tom Campbell

Grzegorz Buczkowski, a Purdue University research assistant professor of entomology, found that odorous house ant colonies become larger and more complex as they move from forest to city and act somewhat like an invasive species, the university said.

“The ants live about 50 to a colony with one queen in forest settings but explode into supercolonies with more than 6 million workers and 50,000 queens in urban areas,” the university explained.

“This is a native species that’s doing this,” said Buczkowski, whose results are published in the early online version of the journal Biological Invasions.


Odorous house ant photo by Noodle snacks/Wikimedia Commons

“Native ants are not supposed to become invasive. We don’t know of any other native ants that are outcompeting other species of native ants like these,” Buczkowski said.

“Odorous house ants live in hollow acorn shells in the forest. They’re called odorous because they have a coconut–or rum-like smell when crushed. They’re considered one of the most common house ants, Purdue said.

In semi-natural areas that are a cross of forest and urban areas, such as a park, Buczkowski said he observed colonies of about 500 workers with a single queen. “It’s possible that as the ants get closer to urban areas they have easier access to food, shelter and other resources,” he said.

Place to nest, place to eat

“In the forest, they have to compete for food and nesting sites,” Buczkowski said. “In the cities, they don’t have that competition. People give them a place to nest, a place to eat.”

Buczkowski observed the ants in three different settings on and around the Purdue campus.

He said it might be expected that if the odorous house ants were able to multiply into complex colonies, other ants would do the same.

But Buczkowski found no evidence that other ants had adapted to new environments and evolved into larger groups as the odorous house ants have, Purdie said.

“It’s possible that odorous house ants are better adapted to city environments than other ant species or that they had somehow outcompeted or dominated other species,” he said. “This raises a lot of questions we’d like to answer.”

Buczkowski said understanding why the supercolonies form could lead to better control of the pests in homes, as well as ensuring that they don’t outcompete beneficial species.

Future studies on odorous house ants will include studying the ant’s genetics and trying to understand the effects of urbanization of odorous house ants, Purdue said.