Synonym(s): Iridomyrmex humilis (Mayr, 1868)
Adult Description: Argentine ants (Linepithema humile)are medium sized ants with a slender, shiny, smooth body. They are light to dark brown in color. Worker ants are 2-3 mm long and monomorphic (all look the same). Queens are larger (4-6 mm long) and, along with a few workers, a queen may start a new colony of her own. A new colony can be established from as little as one queen and 10 workers. Forming colonies in this way is called budding and allows for much farther and faster distributions.
Larva Description: Argentine ant larvae look like typical ant larvae.
Host Plant: None
Ecological Threat: Argentine ants are most notable as a nuisance pests in urban areas, especially because of the availability of water. This ant exists in back yards in high densities associated with landscape features that provide favorable microclimates, such as potted plants and walkway bricks or stones. They enter homes through cracks and other spaces, in search of food or water.
In addition to being a nuisance in urban settings, the Argentine ant is problematic in both natural and agricultural ecosystems. Argentine ants live cooperatively in large colonies consisting of several nests and queens covering a large area. This arrangement is possible because of unusually low levels of intraspecific aggression, which facilitates high population densities. As a consequence, Argentine ants can outnumber and compete effectively with other insects when foraging for food and habitat. Presence of Argentine ants can displace native ants and severely disrupt natural food webs.
Argentine ants are also an economic threat because of their potential to tend plant pest insects, such as aphids. In return for sweet honeydew secretions from these plant feeding insects, ants provide protection from natural enemies.
Biology: 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. Argentine ants occupy flimsy, unstable nests and move very frequently to maintain a favorable microenvironment for brood rearing.
History: The Argentine ant 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.
U.S. Habitat: 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.
Native Origin: South America: Specifically Brazil and Argentina.
U.S. Present: The Argentine ant has spread all across southern United States, and is found in Arizona, California, Illinois, Maryland, Missouri, Oregon, Texas, and Washington.
Currently the Argentine ant has established populations within Texas. The ant is scattered throughout central and eastern Texas and has been identified in the Lower Galveston Bay watershed in Harris County.
Distribution in Texas:
This ant may be confused for the Pharaoh ant (Monomorium pharaonis) due to their physical similarities.
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.
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.
Bond, W., P. Slingsby. 1984. Collapse of an Ant-Plant Mutalism: The Argentine Ant (Iridomyrmex Humilis) and Myrmecochorous Proteaceae. Ecology 65(4): 1031-1037.
Human, Kathleen G., Deborah M. Gordon. 1996. Exploitation and interference competition between the invasive Argentine ant, Linepithema humile, and native ant species. Oecologia 105(3): 405-412.
Layton, B. and J. A. MacGown. 2006. Control of Argentine Ants and Odorous House Ants in the Home. Mississippi State University Extension Service, Publication no. 2407. 7 pp.
Newell, Wilmon, T. C. Barber. 1913. The Argentine Ant. Washington: Government Printing Office.
Jerry Cook, Ph.D - Sam Houston State University - firstname.lastname@example.org