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How to identify it
- Workers are shiny black and very small, about 1/16 inch (1 to 1.5 mm) long, and all workers in a colony are the same size.[1][2]
- Antennae have 12 segments ending in a 3-segmented club, and the waist has two nodes; you need a hand lens to see either.[1][2]
- Queens are larger, about 1/8 inch. Cornell describes workers as dark brown to black with an uneven thorax in profile.[3]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Pharaoh ant | Similar in size, about 1/16 inch, but light yellow to red rather than shiny black, and in the north central states it nests only indoors.[4] |
| Odorous house ant | Brown to dark brown, about 1/10 inch, with a single waist node hidden by the abdomen; it smells unpleasant, like rotten coconut, when crushed.[4] |
Where it lives
A native ant found across southeastern Canada and the northern and eastern United States, reaching the Pacific Coast; it is common in southern California and the San Francisco Bay area.[1]
Biology and life cycle
Colonies are moderate to large and hold many queens; winged males and females appear in summer.[1][2]
Workers hunt insects and collect honeydew from aphids and other sap-feeding insects. They will eat almost anything, including pollen, bread, grease, oil, meat, fruit, vegetables and sweets.[1][3][2]
Nests are shallow, under debris, wood, small stones and bricks or in open lawn soil outdoors, and in woodwork, mortar, wall voids and under carpets indoors, often near warmth and moisture. UC Cooperative Extension in Ventura County adds flower pots and spots under sidewalks.[3][1][2][5]
Colonies move quickly if disturbed, and UC Cooperative Extension notes they often shift to higher ground as fall rains begin. In California they are most active in summer.[5][2]
In laboratory colonies, queens lived about a year and workers about four months.[1]
Workers carry venom dominated by alkaloids, and USDA researchers have identified more defensive compounds from their stingers. These chemicals may help this native ant compete with red imported fire ants, though one ant's dose of the amines tested was too small to knock down a fire ant.[6][7]
Damage and signs
- A nuisance ant: at high numbers it can spread through a building and invade nearly every crack and crevice.[1]
Health risk
The main concern is ants trailing into food cabinets and pantries and getting into stored food.[1][3]
Control
Prevention
Inspect both inside and outside to find all the nests before treating. More than one wingless worker suggests a nearby outdoor nest, and winged ants indoors suggest a nest inside.[1][3]
Keep them out
Remove litter and objects ants can nest under, and seal cracks in foundations, exterior walls, windows and vents; watch where ants come in and plug those entry points.[1][3][5]
Sanitation
Keep food in sealed containers and surfaces clean, and move plant debris and mulch away from the foundation.[3]
Traps and physical control
An indoor nest can be vacuumed out and the contents destroyed, though Cornell notes this reduces rather than eliminates the ants because not all of them are in the nest at once.[3]
Pesticides
When nests can't be found, place ant baits along foraging trails; don't spray or kill trailing ants, so workers carry bait back to the colony.[1][3]
Outdoor nests can be drenched with a residual insecticide, and nests in wall voids treated through cracks and around baseboards.[1]
Where sources disagree
Colony size: Texas A&M describes colonies of up to 2,000 workers, while Cornell says colonies can grow to 10,000 and that a single nest holds a few dozen to a few thousand ants.[1][3]
Mating season: Cornell says winged ants mate from spring through mid-July, while Texas A&M says only that winged males and females are produced in summer and that mating flights have not been observed.[3][1]
Color: Texas A&M calls workers shiny black, and Cornell dark brown to black.[1][3]
Smell: Cornell's school IPM page says crushed little black ants may smell like rotten coconut, a trait Minnesota gives for the odorous house ant.[3][4]
Spray or bait: Cornell says not to spray while baits are out, so workers can carry bait home. UC Cooperative Extension's archived page advises spraying where ants enter and around the foundation, along with bait stations, and Texas A&M drenches nests once they are found.[3][5][1]
Common questions
- How big is a little black ant colony?
- Texas A&M describes colonies of up to 2,000 workers with many queens; Cornell IPM notes colonies can grow to around 10,000.[1][3]
- Why do I see more ants after putting out bait?
- Ant numbers may rise at first as workers recruit to the bait, then decline slowly as they carry it back to the colony.[3]
Sources
- Texas A&M AgriLife Extension, Urban and Structural Entomology, “Little Black Ant.” urbanentomology.tamu.edu/urban-pests/ants/little_black/ (accessed 2026-11-11)
- Santa Barbara Museum of Natural History, “Monomorium minimum (Ants of the Santa Barbara Museum of Natural History).” research.sbnature.org/SBAnts/m_min.htm (accessed 2026-11-11)
- Cornell Integrated Pest Management with the Northeastern IPM Center, “Little Black Ant, Monomorium minimum (School IPM Best Practices, reviewed February 2020).” schools.northeastipm.org/pests/little-black-ant (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 Cooperative Extension, Ventura County, “Little Black Ant (archived).” ucanr.edu/node/125580 (accessed 2026-11-11)
- Toxicon, via PubMed, “Chen, Cantrell, Oi and Grodowitz (2016), Update on the defensive chemicals of the little black ant, Monomorium minimum.” pubmed.ncbi.nlm.nih.gov/27641747/ (accessed 2026-11-11)
- Journal of Chemical Ecology, via PubMed, “Wang and Chen (2015), Fatty amines from little black ants, Monomorium minimum, and their biological activities against red imported fire ants, Solenopsis invicta.” pubmed.ncbi.nlm.nih.gov/26254063/ (accessed 2026-11-11)
- iNaturalist, “Monomorium carbonarium taxon page (order and family).” www.inaturalist.org/taxa/1404041 (accessed 2026-10-06)