Ants
Why ant spray makes it worse
Repellent ant sprays cause colony budding, which splits one nest into several. Here is what is actually happening and what to do instead.
The short answer
Most retail ant sprays are repellent, and repellents trigger budding in the multi-queen Argentine ants common in Auckland. The colony detects the treated zone as hostile, splits, and establishes satellite nests elsewhere, each with its own queens. One trail becomes several. Non-repellent transfer bait, which the ants carry home and share, is the only approach that reduces the colony rather than fragmenting it.
What you are actually killing
The ants you can see on a bench are foragers, and foragers are a small minority of a colony, typically somewhere under ten percent. The queens, the brood and the great majority of workers are in the nest, which may be in a wall cavity, under a patio, inside a stone wall or several properties away.
Killing foragers therefore does almost nothing to the colony's capacity. It removes the individuals currently out collecting, which the colony replaces. The trail disappears for a day or two and returns, which is the experience nearly everyone has with retail sprays. That is why professional ant control is built around bait rather than spray.
Why repellency is the real problem
Retail sprays are formulated to be repellent because that is what sells. A product that makes ants visibly turn around and leave feels like it is working, and a product that lets them walk over it feels like it is not.
But the Argentine ant, the species behind most bad Auckland ant problems, has many queens and reproduces by budding. When part of the colony detects a hostile zone, the response is not to die, it is to split. A group of workers takes brood and one or more queens and establishes a new nest somewhere the chemical is not. The white-footed house ant already lives in many nests at once, so spraying it only removes the foragers that happen to be on the trail.
That is how a single trail across a kitchen bench becomes four trails in four rooms, and it is the most common reason we are called to an ant job. The situation is entirely recoverable, but it takes longer than it would have if nothing had been sprayed.
How transfer baiting works instead
A non-repellent bait is designed to be attractive and, critically, slow acting. Foragers find it, feed, and carry it back to the nest, where it is distributed through the colony by trophallaxis, the mouth to mouth food sharing ants use to feed each other and the brood.
Because the active ingredient works slowly, the forager survives long enough to get home and pass it on. The bait therefore reaches ants you will never see, including the queens, which is the only way to actually reduce a colony.
The counterintuitive part is that ant numbers usually rise for the first two to four days. That is recruitment to a food source and it means the bait is being accepted. Numbers then fall away. If you are choosing a bait yourself, we have set out how ant bait works instead of a spray, and which kind suits which ant.
What is the best spray for ants, if you are going to spray anyway?
If you are going to spray, do it outdoors only, on the ants nest itself or as a perimeter band around the base of the house where the trail comes in, and choose a non-repellent product rather than a fast knockdown surface spray. Never spray a trail that is being baited, and do not spray inside the house at all, because indoors a spray only scatters the ants into the walls.
Read the label before the application, not after, and follow it exactly: it sets the rate, where the product can go and how long to keep pets and children off the treated area. Wear gloves when mixing or applying, keep spray off vegetable gardens and anything that runs to a drain, and store the container out of reach. If the ants are coming in through a single entry point, sealing that gap after the colony has been baited will often do more than any spray.
What to do, and what not to do
Do not wipe the trail, spray it, or clean along it with disinfectant while baiting is under way. The trail is the delivery route, and disrupting it interrupts exactly the process you want.
Do not use a repellent spray anywhere near bait placements, because it makes the bait unattractive and can stop the treatment working entirely.
Do deal with what is feeding them outdoors. Ants farming aphids or scale insects on a citrus tree, a hedge or a shrub against the house have a reliable honeydew supply that will keep a colony resident regardless of what happens in your kitchen.
Do fix any moisture source. A trail heading to a bathroom or laundry rather than to food is usually about water, and it often marks a slow leak behind a cabinet or a failed shower seal.
Questions
Ant spray and ant killer questions
What is the best ant killer in New Zealand?
The best ant killer is the one the colony eats and carries home, which means a slow-acting bait rather than a spray. Indoors that is a gel or liquid bait placed on the trail; outdoors, a granular bait near the nest. Borax mixed weakly into sugar water is the home-made version, and we explain natural ant remedies, and why borax is different. Test sugar against protein first: a colony ignores the wrong one.
Can you get rid of ants for good in New Zealand?
For most ant problems, yes: baiting the colony and then sealing the entry points usually ends it. Argentine ants are the honest exception, because their supercolonies run across many properties and a single house can only be kept clear, not made ant free for ever. Where a whole street has them, neighbours treating at the same time get a much better result.
What do ants hate?
Vinegar, cinnamon, peppermint and coffee grounds are the usual answers, and they work only in the sense that wiping a trail with vinegar or soapy water removes the scent the ants follow, so the line breaks for a while and then reforms from the same nest. As repellents they have little evidence behind them, and anything that pushes Argentine ants away risks the same splitting a spray causes.
I already sprayed. Have I ruined it?
No, but it will take longer. Tell whoever treats it what you used and where, because residual repellent affects where bait can usefully be placed and how quickly it will be accepted. If the colony has already budded there may now be several nests to deal with rather than one.
How long should baiting take to work?
Expect numbers to rise for two to four days, then fall. Most household ant problems are substantially reduced within one to two weeks. Large multi-nest situations, which is what Argentine ant supercolony conditions produce, take longer and often need staged treatment.
Can Argentine ants be eliminated completely?
Not from a neighbourhood. Argentine ant colonies do not fight each other, they merge, so a supercolony can span many properties and streets. What is achievable is sustained control of the population using your building plus a real local reduction. Where several neighbouring properties treat in the same window the result is markedly better.
More advice
Other things worth knowing
Argentine ants in Auckland: how to tell, and what actually works
How to tell Argentine ants from other Auckland ants, why their supercolonies refill a cleared house, when they peak, and what works against them.
Read this AntsHow to get rid of ants in the house
A practical order of work for ants in the kitchen, in the walls or nesting inside the house: find where they come in, bait them properly, then seal the gap.
Read this AntsDoes ant bait work, and which kind should you use?
Which ant bait suits which ant: gel, liquid, granules and bait stations compared for New Zealand homes, why bait beats spray, and when DIY stops working.
Read thisNot sure what you are dealing with?
Describe it, or send a photograph. Identifying it correctly is our job, and it is what decides the treatment.