Ants in Adelaide homes: five species, very different problems

Ants are easily the most common pest complaint in Adelaide homes, and also the most misidentified. The supermarket aisle has a single "ant spray" and that is roughly how most homeowners think about the problem. In practice the five species you are most likely to encounter behave so differently that a single approach is rarely effective against more than one of them at a time.

Coastal brown ants and Argentine ants are by far the most common indoor invaders. Both form supercolonies with multiple queens and many nest sites, which is why knocking out one trail in the kitchen rarely solves the problem. White-footed house ants and garden ants make seasonal appearances. Carpenter ants are the species that actually matters to the building, and they nest exclusively in damp or already-rotted timber. Their presence is a useful biological flag that there is a moisture or decay issue worth investigating.

An inspection is not about killing ants on the day. It is about identifying the species, locating the nest pathway, and flagging the conducive conditions (food access, water, decaying timber) that are sustaining the colony. Treatment is a licensed-technician job that follows the inspection.

Wall cavities: the most common indoor nest site for coastal brown and Argentine ants. The colony lives inside the cavity and workers exit through cracks in cornices, around power outlets, or through gaps at the floor-skirting junction. The trail you see is the highway, not the nest.

Under slabs and paving: mounds of fine soil pushed up through cracks or expansion joints. A colony nesting under the slab or driveway will forage indoors through weep holes and slab penetrations. Easily mistaken for termite mudding by the untrained eye.

Gardens and mulched beds: the standard outdoor nest for most species. Garden ants live in soil mounds; coastal brown and Argentine ants nest in disturbed soil under mulch, retaining walls, and around irrigation infrastructure.

Subfloor: dark, undisturbed timber subfloors are common harbourage. Carpenter ants specifically target damp or decayed bearer and joist timber. If you find a carpenter ant nest under a bathroom or laundry, there is almost always an upstream plumbing leak feeding the moisture problem.

Roof voids: less common than subfloor but still flagged. Argentine ants in particular establish nests around chimney flashings, plumbing penetrations, and concealed roof-cavity timber.

Eaves and wall cladding: behind weatherboards, in soffit cavities, and inside exterior trim. Trails appearing on the outside walls of the home often originate inside this concealed space.

Repeated supermarket bait failures: if two or more rounds of shop-bought bait have not stopped the trails, the colony is larger or has more nest sites than the bait can reach. Time for a proper identification.

Ants inside walls or ceilings: trails that originate from inside the building (rather than entering from outside) point to a wall-cavity or roof-void colony. These will not respond to perimeter sprays.

Large slow-moving black ants indoors: the visual signature of carpenter ants. A carpenter ant inspection is also a moisture and timber-decay inspection.

Multiple species at once: the supermarket spray rarely handles two different species effectively. An inspection identifies all species present and prioritises the treatment order.

Pre-purchase: ant species can be a useful tell on the building condition. Carpenter ants in the subfloor are a serious finding. Argentine ant supercolonies are an ongoing maintenance issue. Document both before contracts exchange.

Commercial food premises: any food-handling business with visible ant activity needs a professional report (and an action plan) for health-compliance reasons. An inspection is the first step.