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Argentine Insects Once Again Making North County Antsy

JULY 27, 2003

By Gig Conaughton, North County Times

It's that time of year again. It's hot, it's dry. And somewhere outside your home, tiny, six-legged scouts are looking to get inside so they can turn that leftover food on your countertop into a wiggling black mass.

Ants, ants, ants ---- particularly Argentine ants, those eighth-of-an-inch-long lovers of all things sweet ---- are once again driving residents crazy in Southwest Riverside and northern San Diego counties.

Sprays and pesticides are flying off store shelves. The phones of pest-control men are ringing off the hook.

And, biologists and pest control experts say, you can't really stop them; you can only hope to contain them.

Experts say there are things you can do to keep them out of your house. But even then, they say, you are not totally safe. They're here. They outnumber us, and they want in.

The problem

California has lots of different types of ants that have annoyed homeowners for years ---- the carpenter ant, the odorous house ant, the pharaoh ant and the thief ant.

But insect researchers and pest control workers said the Argentine ant ---- an insect that doesn't belong here and is aggressively pushing out native ant populations ---- is the king of California's ant pests.

David Holway, an assistant professor of biology at UC San Diego who has studied the Argentine ant, said the insect is indigenous to South America, and was first ferried to the United States accidentally by cargo ships bound for Louisiana in the mid-1800s. By 1891, it was discovered in California, where it has since become an increasing nuisance.

Interestingly, most of Southern California is inhospitable to Argentine ants because it is so dry. Holway said they probably would not be found here at all except for the fact people have invited them, creating the perfect ecosystem for the ants by turning desert chaparral and coastal sage scrub habitats into artificially wet gardens and lawns.

"They like places that are moist," Holway said. "They can't get into areas that are very dry. That should be one of our saving graces here. (But) they're certainly in people's homes and yards. We irrigate."

The primary reason Argentine ants invade our homes every summer, Holway said, is because they're looking for water as Southern California's semi-arid climate heats up and dries out their nests.

But while water is their main driver, Argentine ants also swarm anything sweet. In their native counties, they are also known as "sugar ants." The ant populations build up in the spring and early summer at the same time there are high populations of honeydew-producing insects such as aphids, mealybugs, psyllids and scale insects in people's gardens. When the summer heat dries up those populations, the ants begin foraging for food.

One tough ant

"They're a tough ant to control," said Tom Veden, a technical specialist with Terminex, the pest control company that operates in 14 countries. "They don't really bite, per se, and they don't vector any diseases ---- like, for example, cockroaches ---- but they're a nuisance. Once they get into something, like a box of brown sugar or something, they wreck it. You have to throw it out."

Argentine ants have thrived in the United States in part because there are no natural predators for the insect here, such as the parasitic wasps that feed on the ants in South America.

But Holway and pest control officials said there are several unique features about Argentine ants that give Argentine ants advantages in tussles with both pest-control workers and native ants competing for food and territory.

First, Argentine ants form what are known as "super colonies," a feature that makes them --- unlike most other species of ants ---- one big happy family with overwhelming numbers, willing to work together.

"Usually, you put ants (the same species) from two different colonies together and they'll fight," Veden said. "But (Argentine) ants pretty much just get together and work with each other."

Holway said you could take a colony of Argentine ants from San Diego, and plop them down with Argentine ants in Sacramento, Davis or San Francisco, and they would work together.

In practical terms for a homeowner dealing with an infestation, it means that even if you successfully kill off a nest, another colony of Argentine ants are likely to show up in the same area and re-invade.

The second feature that makes Argentine ants so tough is the fact that unlike many other species, they have multiple queens, the female ants that lay eggs and keep the colony alive.

"They're egg-laying machines," Veden said.

According to documents from the UC Davis' department of pest management control, a colony of the bothersome carpenter ant can contain "several thousand" individual ants. In contrast, a single colony of Argentine ants can contain "millions of ants, and several subcolonies."

Lastly, Holway said, Argentine ants are flexible. He said they normally live along streams and rivers in South America, where seasonal flooding often forces them to move their nests. Because of that, he said, the ant is not discouraged when it is forced to leave one location in your yard or home by pesticide-spraying homeowners or pest-control workers.


Glenn Brank, spokesman for the California Department of Pesticide Control, said if people must resort to using insecticides, they should remember to use common sense.

Read and follow the directions on labels. Make sure that you get the right insecticide. It might not work, Brank said, to use a pesticide aimed at wasps if you're trying to kill ants. Keep pets and children away from the area you're spraying, and when you're done, make sure you store the pesticide in places and containers where children and even unsuspecting adults won't find them.

"You would be amazed at how often people put (pesticides) into old food containers and leave them on kitchen counters," Brank said. "It's unbelievable but true.

"I remember a couple of years ago some guy had used this spray product and put it in the bathroom cabinet. Then his wife came in and grabbed it thinking that it was her hair spray. It wasn't a fatal accident, but it was an injury that required medical attention."

Gary Siebenforcher, a sales associate in the garden center at the North Oceanside Home Depot, said that customers have been flocking in to buy ant-fighting sprays, baits and traps. Baits are more effective than sprays because the ants take the bait back to their nests, killing the queens and other members of the colony.

Siebenforcher said his favorite tip is telling customers to use boric acid on the inside of their interior and exterior walls. The weak-acid powder is sometimes used as a mild antiseptic. Like baits, the ants track the boric acid back to their nest.

"Just take the light switch off and squirt it into the walls," Siebenforcher said. "They'll (ants) track through it and bring it back to their nest. They're going through our inner walls to get food and water. A bottle of boric acid goes for like $3."

Siebenforcher said people should remember to turn off the electricity at the fuse box to prevent getting shocked. In addition to boric acid, Siebenforcher said a lot of customers are buying Malathion, a stronger insecticide used mainly for outdoor spraying.

However, Siebenforcher and Dale North, a certified horticultural pro at the Home Depot in East Escondido, both said they recommend that customers with real ant problems invest in paying for a routine spraying done by professional pest-removal companies.

It could be worse

Meanwhile, Holway, the biology professor from UCSD, said Southern California residents may one day remember fondly the problems they used to have with Argentine ants. He said that's because Argentine ants could be replaced themselves within the next decade by a more terrifying alien invader ---- the red imported fire ant, an aggressive ant with the bite of a wasp sting.

The red imported fire ant is common in 11 southern states; it found its way to California in 1998, and has caused Orange County to be placed under a state quarantine.

"The Argentinian ant was introduced into the south before the fire ant. And nobody talks about the Argentinian ant in the Southeast," Holway said. "And that implies that (fire ants) out-competed the Argentinian ants.

"And fire ants sting," he said. "Argentinian ants don't sting."

Contact North County Times staff writer Gig Conaughton at (760) 739-6696 or

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Originally published on July 27, 2003 at