Why pavement ants like driveways
Pavement ants (Tetramorium immigrans) prefer hardscape edges — the joint between concrete slabs, the gap between pavers, the seam at a wall-walkway interface. The cover provides protection from predators and stable temperature. The soil immediately below is soft enough to excavate. Most BC residential properties have pavement ant colonies somewhere on the lot; they're usually invisible until they push soil up to a visible seam.
Pavement ant biology: what you're actually looking at
Tetramorium immigrans is a European introduction that has colonized most of North America, arriving in the Pacific Northwest in the early 1900s via shipping. Workers are dark brown to black, 2-3 mm long, and slow-moving compared to some other species. A single colony holds 3,000-5,000 workers and one or a few queens. Pavement ant colonies are highly territorial — the 'ant wars' you sometimes see on driveways in summer (large aggregations of ants fighting) are territory conflicts between adjacent colonies. These battles are spectacular but harmless.
When to treat
- Trails entering the home: bait the indoor trail; the colony declines.
- Pavers destabilizing because of nest excavation: rare, but treat if happening.
- Cosmetic preference (don't want soil mounds visible): outdoor exclusion is challenging — sealing seams temporarily disrupts but doesn't eliminate.
When to leave alone
Outdoor pavement ants are part of the local invertebrate ecosystem. They aerate soil, prey on smaller insects, and don't damage structures. If they're not entering your home, treatment is mostly cosmetic. Indoor entry typically responds well to a single bait treatment without exterior work — colonies retract to the soil colony when food signals decline indoors.
The indoor-to-outdoor connection
When pavement ant colonies reach populations above about 3,000 workers, they commonly establish satellite foraging routes that extend indoors — typically through expansion joints in the foundation, weep holes in brick veneer, utility penetrations, or door-bottom gaps. The outdoor nest remains the colony home; the indoor trail is a foraging extension. This distinction matters because it means you don't need to treat the outdoor colony — treat the indoor trail and seal the entry, and the outdoor colony stays outdoors without being pushed to relocate.
Distinguishing pavement ants from fire ants
Fire ants (Solenopsis invicta) are not established in BC and rarely intercepted. The pavement ants you see fighting on a summer driveway are not fire ants. Fire ants are reddish-brown (pavement ants are dark brown-black), build large dome-shaped mounds in open soil (pavement ants build at seams under pavement), and have a significantly more aggressive sting response. If you are in Metro Vancouver and see 'fighting ants' on your driveway, they are pavement ants, not fire ants.