Swarms of South American invaders have colonized our parks, apparently oblivious to immigration law.
Worse yet, they're now showing up in our homes.
A young University of Arizona researcher may find the key, however, to controlling colonies of rover ants.
Javier Miguelena did not start his doctoral research in entomology to find a solution for the "rover ant" or Brachymyrmex patagonicus problem.
He knew the species had invaded Tucson and would be part of his examination of ant species in Tucson parks, undeveloped urban plots and undisturbed desert.
He did not know that the tiny ants would be such a large part of his dissertation studies.
Now he has begun growing his own colonies of rover ants, and his discoveries may lead to pest-control strategies for a species that seems to easily elude attempts at control, said Paul Baker, a UA outreach entomologist who advises Miguelena.
Little is known about the behavior of rover ants, which began showing up in Southern and Southwestern U.S. cities within the past decade.
They are a nuisance rather than a menace. Only 1/16-inch long, they don't bite or sting, and they don't eat your home. They just show up in large numbers where they find optimal living conditions.
Parks are an obvious lure, said Miguelena.
"We think it is related to the fact they have water almost all year long. That is a great advantage when you are in the desert. Also, food resources, from the plants and also from people," he said.
Most invasive insects have a tough time surviving in our climate, Miguelena said, because they require more water than the desert provides. But parks, and our irrigated yards, provide an environment closer to their native one. The ants are believed to be tropical in origin, but their origin has not been pinpointed, said Miguelena.
Miguelena set traps at 36 sites, 12 each in city parks, urban fragments of undeveloped land and more pristine desert.
He's found the most species at parks, and the rover ants are far and away the biggest species. He has also found the rovers in his fragment traps but none in unspoiled areas.
After finding so many rover ants, he decided to colonize some and easily gathered up queens from the UA campus, where conditions are also ideal.
Rover ants haven't been a major problem in Southern Arizona but, when they do show up, they are difficult to treat, said Bob Hartley, former vice president of technical services for Truly Nolen Pest & Termite Control.
His company had a problem removing ants that had invaded the intensive-care unit of a hospital, he said, until it discovered the source of moisture.
A layer of plastic was trapping moisture beneath the landscaping rocks just outside the walls of the ICU. "I believe we got that problem resolved," said Hartley.
Dan Atkins of Johnston's Pest Solutions said the rover ants "definitely require moisture and something sweet to eat."
He hasn't encountered a lot of them, he said, but they are "a challenge" because of their small size. "It's good they're doing research," he said, "because there is not a lot of information out there."
Most infestations of non-native ants result from a too-moist environment, Hartley said. "It's like building a terrarium for a species that really can't live here."
Rover ants may have other characteristics that make them proliferate, said Miguelena.
For one thing, they seem to be overlooked by larger native species, which are often very antagonistic toward newcomers.
They do fight with other rover ants from different colonies, Miguelena said, which should keep them from forming hard-to control "super-colonies" with multiple queens.
He has found, however, that they form their own satellite colonies.
In the lab, he is experimenting with different lengths of see-through tubing to see how far afield these satellite colonies might be located.
With so little known about the ants, said Baker, the UA outreach entomologist, Miguelena has positioned himself at the "cutting-edge" of research into them.
It's a change for Miguelena, who said he wasn't much interested in ants when he did his undergraduate work at the Universidad de las Américas in Puebla, Mexico.
"I'm a biologist. I knew I wanted to study insects, and at first I didn't like ants that much because they're very small. They're very hard to collect and then to observe and then to look at all the tiny parts."
Now, however, he's on his way to becoming an authority on one of the tiniest species of all.
"I'm a biologist. I knew I wanted to study insects, and at first I didn't like ants that much because they're very small. They're very hard to collect"
Contact reporter Tom Beal at email@example.com or 573-4158.