Ants in the kitchen: why they come back and what actually works

Ants are very good at their job. A single scout finds a smear of jam on the bench, heads home laying a scent trail, and within an hour there is a line of workers from the skirting board to the toaster. Spray them, wipe them away, and the next day they are back.

That is not bad luck. It is how ant colonies work, and once you see why, the fixes make more sense.

Why they come back

The ants you see are foragers, sent out to find food and water for a nest you cannot see. That nest might be in the garden, under paving, in a wall cavity or beneath the house. Killing the foragers on the bench removes a few workers; the colony simply sends more along the same scent trail.

So there are really only two lasting approaches: make the kitchen less rewarding to visit, and, when that is not enough, reach the colony itself.

Follow the trail first

Before you clean anything, spend five minutes watching. Where do the ants come in? A gap where the bench meets the wall, a crack in the window frame, a hole around a pipe under the sink, the edge of a door? Where are they going: the sugar, the cat bowl, the rubbish, a sticky bottle, the sink? Knowing both ends of the trail tells you what to remove and what to seal.

The bench habits that help

• Wipe the trail away with warm soapy water. The University of California’s ant guide recommends cleaning up invading ants with a sponge and soapy water as soon as they arrive, because it removes the scent trail that leads the next ones in.
• Seal sweet things. Sugar, honey, jam, syrups, cereal and biscuits in jars or containers with good lids. Wipe sticky jars and bottles before putting them away.
• Do not leave pet food out. Lift the bowls between meals, or stand the bowl in a shallow dish of water as a moat.
• Rinse recycling and empty the bin more often while ants are around.
• Deal with water. In dry spells ants come in looking for water as much as food. Fix drips and dry the sink at night.
• Seal the way in. A bead of silicone or caulk along a gap at the back of the bench, or around a pipe, can stop a trail entirely.

Baits, not sprays

The University of California guide is blunt about indoor sprays: spraying ants indoors does not stop more ants from coming in, and sprays only give temporary control. Baits work differently. They mix a slow-acting insecticide with something the ants want to eat, and the workers carry the bait home to share with the rest of the colony, including the queens. That is why baits take days to work, and why it is a mistake to spray the ants feeding on a bait station.

How to use them well:

1. Put baits on or right next to the trail, out of reach of children and pets.
2. Leave the ants alone while they feed. A busy bait station is a good sign.
3. Keep the bench clean of other food so the bait is the best thing on offer.
4. Give it time. Expect numbers to drop over several days to a week or two.
5. Try a different bait if they ignore it. Some ants prefer sweet baits, others protein or oily ones, and their preference can change with the season.

Many ant problems are best handled outside, where the nests are. The University of California guide suggests baiting outdoors to reach the colony.

Argentine ants: when it is bigger than your kitchen

Most ants seen in New Zealand homes are black. If yours are honey-brown, small, and moving in wide, fast, multi-lane trails, they may be Argentine ants. The Department of Conservation’s Argentine ant page describes them as one of the world’s worst invasive species, known in many parts of Auckland, Northland, Waikato, Bay of Plenty, Hawke’s Bay, Wellington, Nelson and Christchurch.

They are hard to control for a particular reason: their nests cooperate with each other and form supercolonies that can stretch for hundreds of metres. DOC notes that using the wrong amount of pesticide can give some nests a sublethal dose and split the colony, making it harder to control. It recommends fipronil-based baits outside the house, multiple bait stations near established trails along paths, fences and garden edges, keeping gel and paste baits out of the sun, and for larger infestations, coordinating with neighbours.

DOC also asks people to avoid moving them around: check bagged garden soil, bark, building materials and outdoor gear before moving them to a new place.

When to call someone

Most kitchen ant visits settle down with clean benches, sealed food and a week of baiting. Get help from a licensed pest controller when:

• you suspect Argentine ants and they are across your whole section; an Argentine ant specialist can treat the wider colony,
• ants are nesting inside the walls, the roof space or electrical fittings,
• baits have not made a difference after a couple of weeks,
• or you rent, in which case talk to your landlord. Tenancy Services’ pest guidance explains how responsibility is usually shared.

Ask any contractor to use baits and targeted treatments rather than blanket spraying, which the University of California guide also recommends. The aim is the colony, not the trail.