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How to identify it
- Sources differ on size: UC IPM and Texas A&M put workers at about 1/8 inch, while Clemson says about 1/16 inch. UC describes them as dull brown and Texas A&M and Clemson as light to dark brown. All workers in a colony are about the same size.[1][4][2]
- One node at the waist. Clemson adds that the thorax looks uneven from the side and that queens are at least twice as long as workers.[1][2]
- Long trails of thousands of ants may run from nests to food. Clemson says trails may stretch 200 feet or more.[1][2]
- They have no stinger but may bite when provoked. Clemson says crushed workers may give off a musty odor, but odor alone isn't a reliable test.[2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Odorous house ant | Darker, brown to shiny black, and gives off a strong odor when crushed. Clemson says the two are often confused and describes the odorous house ant's smell as rotten coconuts, while an Argentine ant may give off only a musty odor.[1][2] |
Where it lives
Nests outdoors in shallow soil just below the surface, deeper in dry conditions, often near buildings, sidewalks and plants with honeydew-producing insects; it enters buildings for food and water or to escape hot, dry weather or flooding.[1]
Biology and life cycle
Colonies aren't separate but linked into one large supercolony with many queens; new queens leave accompanied by workers. Texas A&M says queens lay as many as 60 eggs a day, workers take about 74 days to develop from egg to adult and live about 12 months, and winged males and females appear in spring and apparently mate in the nest, since mating flights have never been observed.[1][4][2]
Ants from different nests are not aggressive toward each other. A genetic study found that introduced Argentine ant populations have lost much of the genetic diversity of native ones, and that this goes with low aggression between nests and lets them form huge, dominant supercolonies.[4][5]
Not every introduced population behaves the same way. A 2004 study found no aggression between colonies in California, but strong aggression and more genetic variation between colonies in the southeastern United States.[6]
Texas A&M says large colonies often split into several in spring and summer, and in fall they come together into large overwintering supercolonies. Clemson likewise says colonies may combine in winter and divide again in spring or summer.[4][2]
It feeds on sweets year-round and on proteins mainly in spring. Clemson says they prefer sweets but are not picky, also taking meats, fruits, dairy products, eggs, animal fats and vegetable oils.[1][2]
Outdoors it tends aphids, scales and mealybugs for honeydew and protects them from natural enemies, leading to outbreaks of those plant pests.[1][2]
Nests are shallow and flimsy, and the ants move them often. Texas A&M says they nest in moist but not wet places: indoors near water pipes, sinks and potted plants, and outdoors under stones and boards, beneath plants, in rotting limbs and stumps, and along sidewalks.[1][4]
Damage and signs
- Invades kitchens and bathrooms for sweets and water and increases aphid and scale damage on landscape plants. Clemson says they may crawl into stoves, refrigerators, shelves, beds and clothing, and food they have fed on may need to be thrown out because they also feed on garbage, sewage and dead animals.[1][2]
Health risk
Argentine ants have no stinger and, like most ants, rarely bite; their impact is mainly as a nuisance indoors and by boosting honeydew-producing plant pests outdoors.[1][2]
Control
Prevention
Keep plants, grass and mulch several inches from the foundation, fix leaky faucets and sprinklers, and manage aphids and scales whose honeydew feeds ants. Clemson adds clearing ground clutter such as boards, lumber piles and decaying plant material, and watering lawns and flowerbeds less, since moist conditions favor the ants.[1][2]
Keep them out
Follow trails to where ants enter, then caulk cracks around foundations and where pipes and wires come in; ants like to trail along wires and pipes. Clemson also suggests trimming tree limbs that touch the house or electrical wires.[1][2]
Sanitation
Store sugar, syrup, honey and pet food in closed containers wiped clean on the outside, rinse soft drink cans, clean up grease and spills, and take garbage out daily.[1]
Vacuum trails or wipe them with soapy water, which removes the scent trail; indoor sprays usually aren't necessary.[1]
Traps and physical control
Keep ants out of trees and shrubs with a sticky band on the trunk (over a protective wrap on young trees) and by trimming branches that touch buildings.[1]
Pesticides
UC research supports low-concentration liquid borate bait (about 0.5 to 1% in sugar water) in refillable stations placed outdoors in shady spots along trails, at least one per side of the house; results take several days to a week. Prepackaged 5.4% borate stations kill foragers but are less effective against large infestations.[1]
Place baits outdoors, 10 to 20 feet apart around the foundation, and keep them filled; treat in late winter and early spring when populations start growing.[1]
Indoors, Clemson says baiting is the preferred treatment: put baits at the closest point where ants are entering, make sure they are feeding, and don't disturb or spray ants at the bait, since they need a few days to carry it back to the queens.[2]
Perimeter sprays kill only foragers, can trap ants indoors, and ants quickly rebuild; avoid granular contact insecticides that look like baits. Texas A&M takes a different view for professional programs: where Argentine ants are numerous and dominant, it says a perimeter treatment can repel foragers and keep them from reinfesting, and nests that can be found can be drenched with a residual insecticide.[1][4]
When to call a professional
Texas A&M says they are hard to control in buildings over the long term because new colonies quickly move in after others are eliminated, and Clemson says very large infestations may need a pest management professional.[4][2]
More from Clemson Extension
Argentine ants probably reached the United States before 1891 on coffee ships from Brazil and Argentina through New Orleans, and they now occur across most of the southern states and California.[2][4]
Common questions
- Why do Argentine ants keep coming back?
- Their nests are linked into supercolonies with many queens, and sprays kill only foragers, so baits that workers share with the colony work better. Texas A&M adds that when colonies are wiped out in a building, new ones quickly move in.[1][4]
- Should I spray around my foundation?
- UC IPM says perimeter sprays don't give permanent control and are less effective than a bait-based program. Texas A&M disagrees for heavy, ongoing infestations, where it says professional perimeter treatments can help keep foragers out.[1][4]
- Why do Argentine ants suddenly show up inside?
- UC IPM says ants come indoors looking for food and water, warmth and shelter, or refuge from hot, dry weather or flooding, and can appear suddenly when outdoor food runs short or the weather changes. Clemson says Argentine ants may nest under or inside homes when their outdoor habitat is disturbed.[1][2]
Sources
- University of California Statewide IPM Program, “Pest Notes: Ants, Publication 7411 (October 2012).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnants.pdf (accessed 2026-11-11)
- Clemson Cooperative Extension, Home & Garden Information Center, “Argentine Ants.” hgic.clemson.edu/factsheet/argentine-ants/ (accessed 2026-11-11)
- iNaturalist, “Linepithema humile taxon page (order and family).” www.inaturalist.org/taxa/68165 (accessed 2026-11-11)
- Texas A&M AgriLife Urban and Structural Entomology Program, “Argentine Ant, Linepithema humile.” urbanentomology.tamu.edu/urban-pests/ants/argentine/ (accessed 2026-11-11)
- Proceedings of the National Academy of Sciences, via PubMed, “Tsutsui et al. (2000), Reduced genetic variation and the success of an invasive species, Proc Natl Acad Sci USA 97(11):5948-5953.” pubmed.ncbi.nlm.nih.gov/10811892/ (accessed 2026-11-11)
- Molecular Ecology, via PubMed, “Buczkowski, Vargo and Silverman (2004), The diminutive supercolony: the Argentine ants of the southeastern United States, Mol Ecol 13(8):2235-2242.” pubmed.ncbi.nlm.nih.gov/15245397/ (accessed 2026-11-11)