Since its introduction to the United States from South America in the late nineteenth century, the Argentine ant, Linepithema humile, has become a serious agricultural and urban pest throughout much of California and in numerous urban developments in the southeastern U.S. This invasive ant has disrupted ecosystems worldwide by directly displacing other ants (including fire ants) and other insects. Honeydew produced by aphids, scale and whiteflies is an important food source for the Argentine ant. Consequently, Argentine ants can be a serious problem when they tend these insect pests and protect them from natural enemy predation creating a problem in the ornamental landscape.
In the urban environment, Argentine ant colonies can reach high population levels around homes, schools, hospitals, etc. It is the dominant urban ant pest in California and Georgia and a significant localized pest in the other southeastern states such as South Carolina, Alabama, Mississippi, Louisiana, Florida, Tennessee and North Carolina. An urban ant distribution survey in North Carolina in 2000 determined that Argentine ants were present in over 20% of the samples submitted by professional pest control operators (PCOs). Either ants were misidentified earlier or have more recently become a problem in North Carolina as natural and agricultural habitats have been cleared for urban development.
Argentine ants do not bite or sting, but heavy ant activity in the urban landscape creates a nuisance for individuals seeking to spend time out-of-doors. Additionally, foraging workers will frequently migrate indoors in search of food and/or in response to outdoor extremes of drought or flooding. Activity of these ants indoors and outdoors provokes homeowners and businesses to apply remedial pest control themselves or have commercial pest control companies perform the work. Chemical insecticides, alone, without an overal management strategy are often inadequate for the long term.
Workers are about 1/8 inch (2.2 to 2.6 mm) in length. Argentine ants have a constricted petiole with one node and the12-segmented antenna has no club. Workers are usually a uniform light brown to brown in color, are slender-bodied with an oval to somewhat triangular shaped head. Mandibles (jaws) have two large teeth neat the tip followed by a series of small teeth.
The Argentine ant nests in diverse habitats and may support multiple reproductive queens in a colony. Related colonies may also be interconnected creating a web-like super population. They nest in soil exposed or protected under mulch, rotten wood, standing dead trees, debris, bird nests, bee hives, and many other places. Indoor nests are often found in walls of bathrooms and kitchens and in crawl spaces beneath the floor. They have a general diet and feed on sweets or fruit and will readily utilize honeydew from certain insects. Indoors they may also feed on grease-containing foods. They can exist in harmony with other related Argentine ant colonies but eliminate competing species within their range. The number of ants in large colonies is almost inestimable.
Landscape infestations may be indicated by heavy ant activity on tree trunks suggesting aphid or scale infestation, or ripening fruit (in fruit trees). Try to treat honeydew-producing aphid and scale insects on these trees or shrubs. Banding the trunk with sticky barriers may also be helpful to reduce colony size. This barrier may need to be inspected and refreshed regularly. Protein based baits are useful, but sugar-based baits are more attractive and effective. Gel baits such as Advion Ant Gel and Maxforce Ant Killer Bait Gel may be used according to label directions. Bait stations may be appropriate outdoors. Bait around each trail, tree base or mound area, if known. Spring is a the best time to treat.
If continual reinvasion is a problem and the colony in not within the home or building, an outdoor chemical barrier sprayed 3-10 feet around the perimeter may be used in combination with an overall management plan. Such chemicals may contain permethrin, bifenthrin, carbaryl or other active ingredients. Read the label regarding the legal band width and whether it allows treatment of the foundation.
Practice careful sanitation procedures indoors. Quickly wipe up any ants found on surfaces with a soapy-water sponge and remove the source of their interest (unless baits are in use). Eliminate any possible attractive food sources and store foods in ant-proof containers. Caulk or block any access points to inside the building such as around doors or windows. Spot treatment using household insecticides labeled for ants may be helpful, but avoid broad, arbitrary use over a large area. Baits are one method of management but are slow acting and will require periodic attention by the applicant. Do not use pesticides at the same time around bait stations. Be careful when moving potted plants from outdoors to indoors that ants are not within the pots. Keep outdoor shrubs, vines and plants from direct contact with the house or building. Remove mulch from alongside of the building if the ants are in the mulch. Colonies in walls will require baits such as Advion Ant Gel, Maxforce Ant Killer Bait Gel, Terro Ant Killer Bait or possible professional treatments injected into the wall space. Argentine ant control may require a long-term pest management program. Outdoor treatment may be required to solve an indoor problem. If you desire a professional pest control company, compare several companies, ask for an estimate and their overall management strategy. Pest Control Operators might use some of the products listed in the NC Chemicals Manual.
Insect notes on ants in Residential, Structural and Community Pests
How to identify Argentine ants. ipm.ucdavis.edu/TOOLS/ANTKEY/argentine.html
Mississippi State publication. http://msucares.com/pubs/publications/p2407.pdf
Global Invasive Species Database http://www.issg.org/database/species/ecology.asp?si=127&fr=1&sts=
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance contact an agent of North Carolina Cooperative Extension in your county.
© 2006 NC Cooperative Extension
Prepared by: Stephen Bambara & Mike Waldvogel, Extension Entomologists and Jules Silverman, Charles G. Wright Professor of Structural Pest Management. Photos by Gissella Vasquez.
ENT/ort-140 December, 2006. Revised with John Brightwell, Postdoctoral Research Asst, NCSU. August, 2010.
Web page last reviewed January, 2011 by the webperson.