Pavement ant

How to recognise it

These are the features that identify a pavement ant. Each one is described in words so the identification works without the diagram.

1. The head and thorax carry fine parallel grooves running front to back, visible under a hand lens as a striped or engraved texture.
2. There are two small spines projecting backward from the rear of the thorax, and two nodes on the waist rather than one.
3. Colour is dark brown to black with paler, often yellowish legs and antennae.
4. Workers are uniform in size at roughly 3 mm.

What it leaves behind

• Small mounds of excavated soil pushed up through cracks in driveways, patios, and sidewalk joints.
• Large numbers of workers on paving in spring, sometimes in mass confrontations between neighbouring colonies.

Why an infestation persists

Nests are outdoors under slabs, stones, and paving, and workers enter buildings to forage rather than to nest. Indoor activity is usually a foraging trail from an outdoor colony, so the entry point matters more than anything found indoors.

Where it occurs

Common across the eastern and midwestern United States and increasingly reported in the West; strongly associated with paved and disturbed urban ground.

Where to look for it

• Expansion joints and cracks in the driveway, patio, path, and garage slab, where small craters of excavated soil mark an active nest below.
• The seam where a concrete step or porch meets the house wall.
• Beneath doormats, paving slabs, and anything flat left on the ground for a season.
• Along the exterior foundation line, especially on the sunniest side of the building.
• Indoors, follow trails back to a floor-level entry rather than searching for an indoor nest, which is usually absent.

When you see it, and why

The conspicuous event is in spring, when neighbouring colonies meet on warm paving and thousands of workers mass in what looks alarming and is in fact a territorial dispute that resolves itself in a day or two. It requires no response at all. Indoor foraging follows the same spring curve and tapers through summer. Because the nest is outdoors and the ants merely visit, activity tracks paving temperature far more closely than anything happening inside the building.

What getting the identification wrong costs you

The consequence of getting this wrong is usually wasted effort rather than harm: people search the kitchen for a nest that is under the driveway. The grooved head and two waist nodes separate it from the odorous house ant, which matters because the two need different handling — pavement ants do not bud, so the approaches that make an odorous house ant problem worse do not have the same effect here.

What it costs

This rarely justifies paid work. The nest is outdoors and accessible, the entry route is usually a single crack, and sealing that crack plus removing the food attractant resolves most complaints for the price of a tube of sealant. If a quarterly contract is being proposed for pavement ants alone, that is the pattern worth declining.