A trail is a supply line with two ends. The end in your kitchen is the symptom; the end where it crosses into the building is the thing to close.
Because there is a nest outside — normal — and something inside worth walking to. The route between the two is almost always a gap where the ground meets the building.
The nest is not the problem. The route is, and closing it is usually a small job once you have found it.
An ant trail is more informative than it looks. Watch it for two minutes before you touch it:
| Entry point | How common | What fixes it |
|---|---|---|
| Patio or path meeting the house wall | Most common | Sealant or mortar along the junction |
| Gap under a back or patio door | Very common | Threshold seal or brush strip |
| Around a waste or service pipe | Common | Silicone sealant |
| Crack in mortar at ground level | Common | Repointing, or sealant as a stopgap |
| Air brick | Occasional | Fine mesh — do not block it |
| Ground-floor window frame | Occasional | Re-seal the perimeter |
| Extension-to-original-building junction | Occasional | Sealant, or a builder if the gap is structural |
One note on air bricks: they ventilate underfloor voids and blocking them entirely causes damp problems. Cover with mesh rather than filling.
See our complete service, published prices and treatment information.
View Ant Control Harrow →Two reasons, and understanding them saves repeated frustration.
The chemical trail persists. Wiping the visible stretch leaves enough elsewhere for the next ant to pick up. Cleaning the whole route — including up the wall and along the skirting — with hot soapy water or dilute vinegar is what actually removes it.
The colony still knows. Even a properly cleaned route leads somewhere the colony has already found worthwhile. Removing the food is what makes the route stop being worth walking.
A pattern people notice and find puzzling. Heavy rain floods shallow nests and pushes activity toward drier ground — which frequently means the sheltered strip against your house, and then inside it.
It usually settles once the ground dries. A trail that only appears after heavy rain is less likely to need treatment than one running through a dry fortnight.
For a few days in warm weather, usually mid-summer, colonies release winged reproductives all at once. It is startling, it happens across the whole area on the same day or two, and it is over quickly.
Not a reason to treat, and not a sign of a new problem.
If you have closed the route, removed the food and cleaned the trail properly and they are still coming in a fortnight later, that usually means either a route you have not found or a colony large enough to keep probing.
Read nextHow Do You Get Rid of Ants in Harrow? →Useful to know where the nest is, but you do not need to find it to close the route or to have the problem treated.
Usually one colony with two routes. Tell us both when you enquire.
A nest in or under the structure is one of the situations where treatment is genuinely warranted. Tell us what you have observed.
Something else appearing outdoors? Wasp nest treatment across Harrow is £90 fixed cost, guaranteed.
The junction where a patio or path meets the wall, and gaps under back or patio doors.
Follow it inside to where it disappears, then look at the same spot from outside. Mid-morning on a warm day is best.
The chemical trail persists elsewhere on the route, and the colony still knows the food is there. Clean the whole route and remove the food.
Cover it with fine mesh rather than filling it — air bricks ventilate underfloor voids.
Heavy rain floods shallow nests and pushes activity toward drier sheltered ground, often against the house.
No. They are the reproductive stage, appear for a few days, and resolve on their own.
Usually one colony with two routes. Mention both when you enquire.
If they are still coming a fortnight after you have sealed the route, removed the food and cleaned the trail properly.
Tell us where they cross into the building. If it sounds like a gap you can seal yourself, we will say so.
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