Argentine ants can develop enormous populations, with large colonies that are comprised of many nests containing hundreds of queens and many thousands of workers. Individual colony members move freely between and within these nests. Queens lay as many as 60 eggs per day. Development from egg to adult averages 74 days for workers. Worker longevity is 12 months. Winged male and female reproductives are produced during the spring. They apparently mate in the nest because mating flights have never been observed. During the spring and summer, large colonies often split or bud-off into several colonies. This splitting occurs when one or more queens accompanied by a group of workers leave the parent nest and find a new nesting site. Ants from different colonies are not aggressive toward one another. In the autumn, colonies often come together to form large over wintering super colonies. During extremely cold weather, these ants become dormant, but they resume their normal activities during periods of warmth. These ants occupy flimsy, unstable nests and move frequently to maintain a favorable microenvironment for brood rearing.
The Argentine ant, Linepithema humile (Mayr), is an introduced species. They are native to Argentina and Brazil. Discovered in New Orleans, Louisiana, in 1891, it is now established in many localities in the southern United States, and is found in Arizona, California, Illinois, Maryland, Missouri, Oregon, Texas, and Washington. It is common in urban settings, but has also become established in rural areas.
Argentine ants are difficult to control within structures on a long-term basis. When colonies are eliminated from a building, new colonies quickly move into the area. Surveys should be made inside and outside buildings to locate all colonies. Argentine ant nests are located in moist, but not wet, areas. Indoors, they are usually near water pipes, sinks, and potted plants. Outdoors, nesting sites include under stones and boards, beneath plants, in fallen and rotting tree limbs, in tree stumps and along sidewalks. They are highly adaptive and can nest in diverse habitats in both covered and exposed soil. Injecting dusts or aerosols through small cracks around baseboards can treat nests inside wall voids. Argentine ant nests located outside can be drenched with a residual insecticide by using a compressed air sprayer. Colonies found living in flowerbeds, mulch, and leaf litter also can be treated in this manner, but with the compressed sprayer at low pressure. When Argentine ants become numerous and are the dominant species, perimeter treatments repel foraging ants and prevent them from re-infesting the property and invading structures. Insecticides used for these treatments should be a wettable powder or micro encapsulated formulation labeled for this type of application. If colonies cannot be located, bait insecticides can be used in stations, placed along foraging trails in numerous locations. Argentine ants are particularly attracted to sweet baits. Regular follow-up visits will determine if bait stations need to be replenished and if colonies have been eliminated.