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How to identify it
- Workers are 1/16 to 1/8 inch long, all about the same size, and uniformly brown to black. Minnesota gives about 1/10 inch and describes them as brown to dark brown.[2][1][6]
- It has one node at the waist, hidden from above by the abdomen.[2][6]
- Crushed workers give off a very strong, rotten odor, a distinctive trait of this species. Minnesota says some people compare the smell to rotten coconuts or blue cheese.[2][1][6]
- Workers move rapidly in single-file trails.[2]
- Penn State notes that the 12-segmented antennae have no club, the thorax is uneven in profile, and there is no circle of hairs at the tip of the abdomen.[2][6]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Argentine ant | Similar size, but dull brown rather than dark brown to shiny black.[1] |
| Pavement ant | Has two nodes at the waist and grooves on the head and thorax, and piles soil at pavement cracks.[3][6] |
Where it lives
Native to most of the United States, from Canada into Mexico. Nests are usually outdoors under rocks and boards or in shallow soil and debris, but colonies also nest indoors in wall voids and near water pipes and heaters.[2][1]
Biology and life cycle
Colonies usually hold several thousand workers with many queens, though they can range from hundreds to many thousands. Texas A&M gives a range of a few hundred to 10,000 ants, usually with multiple queens.[2][5]
Colony size depends on where they live. A 2023 study notes that colonies in natural habitats are usually small, live in one nest and have one queen, while urban colonies have many queens and nests and form large supercolonies.[8]
In a survey of 180 sites, urban plots with odorous house ants held far fewer ant species (7) than urban plots without them (18). The authors suggest city life frees this native ant to grow to supercolony size and crowd out other ants.[7]
Winged reproductives appear from May through July. Texas A&M says winged forms come only from colonies at least four to five years old, and mating may happen in or near the nest.[2][5]
Texas A&M gives development times of 11 to 26 days for eggs, 13 to 29 days for larvae, and 10 to 24 days for the prepupal and pupal stages, varying with the season. New colonies start when queens leave with groups of workers, or from single queens after mating flights.[5]
Workers prefer sweets but also take dead insects and grease; outdoors they feed on aphid honeydew and flower nectar. Minnesota says they also take live insects and will forage indoors for meats.[2][6]
Outdoors they nest in soil under almost any object, such as stones, boards, patio blocks, logs or mulch. Indoors, Minnesota says they nest in wall voids and under floors near moisture, and Penn State says they will nest in termite-damaged wood. Texas A&M notes they move often from loosely built nests.[2][6][5]
Damage and signs
- Workers contaminate food and pantry items.[2]
Health risk
Odorous house ants are a nuisance pest; their main impact is contaminating stored food.[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. Minnesota also says to check for outdoor nests under stones, firewood and bricks and treat any found, and to manage aphids nearby that feed the ants.[1][6]
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.[1]
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]
Pesticides
Use baits made for sweet-feeding ants; slow-acting baits such as those with boric acid, fipronil or hydramethylnon let workers carry bait back to the queens and young. Keep baits stocked and out of reach of children and pets; control can take two weeks or longer.[2]
Don't spray insecticides while baiting, and place baits outdoors near nests and trails when you can, since indoor baits can draw ants inside.[1][6]
Sources differ on bait type. Penn State recommends baits made for sweet-loving ants, while Texas A&M says baits with a protein or sugar attractant may work when the nest can't be reached. Minnesota notes that a colony's food preferences can change during the season.[2][5][6]
When to call a professional
Minnesota says baits can be effective but persistent odorous house ant problems should be handled by a pest management professional. For professionals, Texas A&M describes injecting dust or aerosol into wall voids, drenching outdoor nests, and perimeter treatments that may keep foragers from coming back.[6][5]
Common questions
- Why do these ants smell when I squish them?
- A strong, rotten odor when crushed is the hallmark of the odorous house ant. Minnesota says some people liken it to rotten coconuts or blue cheese.[2][6]
- How long do ant baits take?
- Two weeks or longer; keep baits replenished so workers keep carrying them to the colony. Minnesota allows longer: several weeks to several months to eliminate a colony.[2][6]
- Why are there so many of them around my house?
- In cities, odorous house ant colonies can have many queens and many nests and grow into supercolonies, unlike the small single-queen colonies found in natural areas. One survey linked their presence in urban plots to a sharp drop in the number of other ant species.[8][7]
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)
- Penn State Extension, “Odorous House Ant.” extension.psu.edu/odorous-house-ant (accessed 2026-11-11)
- Penn State Extension, “Pavement Ant.” extension.psu.edu/pavement-ant (accessed 2026-11-11)
- iNaturalist, “Tapinoma sessile taxon page (order and family).” www.inaturalist.org/taxa/47340 (accessed 2026-11-11)
- Texas A&M AgriLife Urban and Structural Entomology Program, “Odorous House Ant, Tapinoma sessile.” urbanentomology.tamu.edu/urban-pests/ants/odorous-house-ant/ (accessed 2026-11-11)
- University of Minnesota Extension, “Ants.” extension.umn.edu/insects-infest-homes/ants (accessed 2026-11-11)
- PLoS One, via PubMed, “Salyer, Bennett and Buczkowski (2014), Odorous house ants (Tapinoma sessile) as back-seat drivers of localized ant decline in urban habitats, PLoS One 9(12):e113878.” pubmed.ncbi.nlm.nih.gov/25551819/ (accessed 2026-11-11)
- Scientific Reports, via PubMed, “Buczkowski, Wang and Craig (2023), Behavioral assays reveal mechanisms of supercolony formation in odorous house ants, Sci Rep 13(1):9013.” pubmed.ncbi.nlm.nih.gov/37268644/ (accessed 2026-11-11)