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How to identify it
- Workers are all one size and extremely small, about 1/32 to 1/16 inch long, so they often go unnoticed; Minnesota calls them the smallest household ants in the north central states.[1][2][3][4]
- They are golden yellow to light brown, usually paler than other tiny ants except the Pharaoh ant.[1][2][4]
- Under magnification: 10-segmented antennae ending in a large 2-segmented club, very small eyes, two nodes in the waist and no spines on the thorax.[1][2][3][4]
- A tiny stinger sits at the tip of the abdomen. Queens are much larger than workers, about 4 to 5 mm.[1][2]
- Minnesota notes that dead thief ants tend to curl up.[4]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Pharaoh ant | Similar size and color, but Pharaoh ants have 12-segmented antennae with a 3-segmented club and normal-sized eyes; thief ants have 10 segments, a 2-segmented club and tiny eyes. A microscope is often needed to tell them apart.[3][5][4] |
Where it lives
A native ant found throughout the United States; Penn State notes it across the eastern states.[1][2]
Biology and life cycle
Colonies are small, from several hundred to a few thousand workers, with many queens.[1][2]
Winged ants mate in flight from late July to early fall (Minnesota gives July through September), and a single mated female can start a new colony on her own; some females have been seen flying with workers clinging to them that apparently help found the nest.[1][4]
In the laboratory, queens laid 27 to 387 eggs a day, and workers took 52 days to develop from egg to adult.[1]
They often nest in or near the nests of larger ants and eat the host colony's food, larvae and pupae.[1][2][3][4]
Outdoors they nest in soil, under stones, logs and bricks, and in decaying wood; indoors, in wall and cabinet voids, under countertops and behind baseboards, where nests are often hard to find.[1][3][4]
They strongly prefer protein and grease, including meats, cheese, peanut butter, nuts, fats, oils, dairy and even dead rodents, but will also take sweets.[1][2][3][4]
Damage and signs
- They invade homes mainly in hot weather, especially mid to late summer, entering through foundation cracks and small gaps in woodwork.[1][2][4]
- Workers travel set trails in cabinets, on walls and along baseboards, and may move between rooms along electrical wiring and through outlets.[3][1][4]
- Their small size lets them get into food packages that larger ants can't enter.[1][3][4]
Health risk
Thief ants have only a very small stinger. The concern is food: the U.S. Food and Drug Administration counts the thief ant as one of two ants on its "Dirty 22" list of pests considered possible carriers of foodborne disease, and their presence in food plants and storage is treated as a sign of unsanitary conditions.[2][6]
Control
Prevention
Confirm whether you have thief ants or Pharaoh ants before treating, because the right control approach differs greatly between the two.[1]
Pesticides
Use slow-acting baits made for protein- and grease-loving ants; Penn State names hydramethylnon, fipronil and boric acid baits, which workers carry back to the colony. Minnesota calls baiting the most effective method when nests are indoors.[2][4]
Place bait where ants are active and out of reach of children and pets, and keep replacing it; control can take two weeks or longer.[2][1]
Once nests are located, outdoor colonies can be drenched with a residual insecticide, and wall-void colonies treated with an aerosol or dust through cracks or small drilled holes.[1]
When ants are coming in from outside nests, Minnesota suggests treating the building perimeter.[4]
When to call a professional
Finding the nests can take considerable time because workers are tiny and appear only now and then; insecticides have worked less well on thief ants than on other species.[1]
A group of look-alike species
Thief ants belong to a group of closely related, little-studied species; Solenopsis molesta is the best known and is used here as the example.[1]
A 2020 genetic study found that one member of the molesta group, Solenopsis abdita, native to Florida, has spread far beyond its native range: samples from Guatemala, Hawaii and Saudi Arabia belonged to it, and the Saudi population had been described as a separate species.[7]
Where sources disagree
Size: Texas A&M and UC IPM give about 1/32 inch, Minnesota about 1/20 inch, and Penn State 1/16 inch.[1][3][4][2]
Range: Texas A&M says the thief ant ranges throughout the United States, while Penn State describes it across the eastern United States.[1][2]
Finding nests: Texas A&M says treatment is fairly simple once nests are located, while Minnesota says locating and treating nests is not practical and that ants foraging in from outside will eventually go away on their own if ignored.[1][4]
Common questions
- Why are they called thief ants?
- They nest close to other ant species and raid those nests for food, eggs, larvae and pupae.[2][1][4]
- Are thief ants the same as Pharaoh ants?
- No. They look alike, but thief ants have 10-segmented antennae with a 2-segmented club, while Pharaoh ants have 12 segments with a 3-segmented club.[3][5][4]
- What bait works on thief ants?
- Choose a bait made for protein- or grease-feeding ants rather than a sugar bait, since thief ants strongly prefer protein.[2]
- Why are they called grease ants?
- Grease ant is another name for the thief ant, which prefers greasy and protein foods such as meats, cheese, peanut butter and nuts.[4][3]
Sources
- Texas A&M Center for Urban and Structural Entomology, “Thief Ant.” urbanentomology.tamu.edu/urban-pests/ants/thief/ (accessed 2026-11-11)
- Penn State Extension, “Thief Ant (updated June 24, 2026).” extension.psu.edu/thief-ant (accessed 2026-11-11)
- University of California Statewide IPM Program, “Key to Identifying Common Household Ants: Thief Ant.” ipm.ucanr.edu/TOOLS/ANTKEY/thief.html (accessed 2026-11-11)
- University of Minnesota Extension, “Ants.” extension.umn.edu/garden-and-home/home-maintenance/household-insects/ants (accessed 2026-11-11)
- University of California Statewide IPM Program, “Key to Identifying Common Household Ants: Pharaoh Ant.” ipm.ucanr.edu/TOOLS/ANTKEY/pharaoh.html (accessed 2026-11-11)
- Journal of Food Protection, via PubMed, “Sulaiman, Anderson, Oi, Simpson and Kerdahi (2012), Multilocus genetic characterization of two ant vectors (Group II "Dirty 22" species) known to contaminate food and food products and spread foodborne pathogens.” pubmed.ncbi.nlm.nih.gov/22856568/ (accessed 2026-11-11)
- Scientific Reports, via PubMed, “Sharaf et al. (2020), Molecular phylogenetic analysis and morphological reassessments of thief ants identify a new potential case of biological invasions.” pubmed.ncbi.nlm.nih.gov/32694527/ (accessed 2026-11-11)
- iNaturalist, “Solenopsis molesta taxon page (order and family).” www.inaturalist.org/taxa/1405138 (accessed 2026-10-06)