Argentine ants in Auckland: why they're so hard to shift

How to recognise them

Argentine ants are small, around 2-3mm, and an even light-to-mid brown. They move in dense, steady trails rather than meandering individually, and they give off a musty smell when crushed.

Trails along fences, paving edges, walls and into kitchens and bathrooms are typical. If you see unusually heavy, persistent trails, Argentine ants are a good suspect.

Why they're different

Most ant species keep to a single nest and defend it against neighbours. Argentine ants don't. Separate nests cooperate and merge into supercolonies, with many queens, that can span whole streets or suburbs.

That's why treating your own property can feel pointless. You can clear the ants on your section while a huge population next door simply refills the space. They also displace native insects wherever they establish.

Why they come inside

Usually food and water. Sweet foods, pet bowls and spills are the draw, and dry spells push them towards moisture indoors. Heavy rain can flood outdoor nests and send them looking for somewhere dry, which is why a trail can appear after a downpour.

What realistically helps

The goal is to reduce numbers and keep them out of the house, rather than to eliminate the whole population.

• Use bait the ants will carry back, and keep it topped up while activity continues
• Seal the gaps they're entering through - around pipes, window frames and cladding
• Cut back plants and mulch touching the building
• Remove food, pet bowls overnight and sources of moisture inside
• Where neighbours have the same trouble, treating at the same time works far better than treating alone