Tetramorium immigrans Santschi, 1927

Pavement ant

The sidewalk ant, tiny, dark, and famous for springtime turf wars between rival colonies.

Order: Hymenoptera
Family: Formicidae
Group: Ants
Ontario status: Introduced, established provincewide

Why it matters

Mostly a nuisance, it contaminates food and is persistent indoors, but it does not damage structures or sting. Its sheer numbers make it the most complained-about ant in Ontario homes.

Origin

Introduced from Europe centuries ago; now one of the most common ants in North American cities.

Behavior

Forages in trails day and night. In spring, neighboring colonies fight spectacular battles on sidewalks, thousands of ants locked in combat.

Living conditions

Nests under sidewalks, driveways, patios, stones and building foundations, anywhere with sun-warmed pavement or soil. Enters homes through cracks in slabs and foundations.

Signs of presence

Small dark ants trailing along baseboards, especially in spring
Tiny soil mounds pushed up between patio stones or along foundations
Mass battles of ants on sidewalks in spring

Weaknesses

Nests are shallow and accessible under pavement edges
Foraging trails are visible and traceable to the nest
Colonies fight each other, limiting unchecked spread

Myths and facts

Myth The spring ant wars mean there is one giant colony.
Reality The battles are rival colonies fighting, pavement ants are fiercely territorial between nests.

Research notes

Morphology

Workers 2.5-4 mm, dark brown to black. Head and thorax with fine parallel grooves (rugae). Two-segmented waist (petiole + postpetiole). 12-segmented antennae with 3-segmented club. Propodeum with a pair of small spines.

Diagnostics

Confirm by small size + grooved head/thorax + two-segmented waist + nesting under pavement with soil excavations.

Easily confused with

Little black ant, Monomorium minimum Little black ant is smaller (~1.5 mm), shinier, and lacks the grooved sculpturing on the head and thorax.
Odorous house ant, Tapinoma sessile Odorous house ant has a single flat waist node and smells of rotten coconut when crushed; pavement ant has two waist segments and no odor.

Life cycle

Adult: Workers live several months; queens live for years.
Egg: Eggs hatch in ~2-3 weeks at warm temperatures.
Egg to adult: ~6-10 weeks at warm temperatures
Generations per year: Continuous brood through the warm season
Nymph or larva: Legless larvae reared in the nest; pupae naked (no cocoons) in Myrmicinae.

Development

Complete metamorphosis: egg → larva → pupa → adult.

Reproduction

Multiple queens per colony (polygynous); mature colonies hold 3,000-10,000+ workers. Nuptial flights in early summer.

Distribution

Global: Temperate North America and Europe
Native range: Europe
Ontario: Introduced; established provincewide in urban and suburban habitats

Ecology

Nests in soil under pavement, stones and foundations; excavated soil forms characteristic crater mounds. Omnivorous, seeds, insects, sweets, grease. Inter-colony aggression ('wars') in spring structures local populations.

Resistance

Limited published data.

IPM implications

Nest location is usually obvious (soil mounds at pavement edges), monitoring should map nest entrances, not just indoor trails. Because colonies are polygynous and long-lived, queen survival determines outcomes; forager-only suppression rebounds. Sealing slab and foundation cracks addresses the indoor interface.

Chemical ecology

Trail and alarm pheromones typical of Myrmicinae; inter-colony recognition via cuticular hydrocarbons drives territorial aggression.

Genetics and DNA

No reference genome published as of 2026.

Taxonomy

Order Hymenoptera, family Formicidae, subfamily Myrmicinae. Described by Santschi, 1927. Introduced from Europe. North American pavement ants were long called Tetramorium caespitum until the 2017 revision of that species complex (Wagner et al.) assigned them to T. immigrans.

Open questions

Whether other members of the Tetramorium caespitum complex occur in North America; colony lifespan in urban heat islands.

References

Hölldobler, B. & Wilson, E.O. 1990, The Ants, Harvard University Press
Mallis Handbook of Pest Control