Pest Control
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The ant marching across your kitchen worktop is almost certainly a black garden ant. It is the most common ant in the UK and the one that comes indoors most often. It is harmless, but a colony that has found a reliable food source in your house will keep coming back until the trail, or the nest, is dealt with.
How to recognise black garden ants
Workers are small, around 3 to 5mm long, and look glossy black or very dark brown. Like all ants they have a narrow waist and elbowed antennae. They do not sting. Queens are much larger, up to about 15mm, but you will rarely see one unless a nest is dug up, or on the summer days when winged queens and males leave the nest to mate.
Workers are active outdoors from around March to October, and most kitchen problems fall in spring and summer. If you are seeing ants indoors in the colder months, read our guide to ants early in the year, because it can mean the nest is closer than you think.
Why ants come into the house
Ants come indoors for food and, to a lesser extent, water. Black garden ants have a strong taste for sugar: crumbs, spilt juice, jam, honey and ripe fruit are all a find. They will also take greasy food, meat, bread and pet food.
When a scout ant finds something worth having, it lays a scent trail of pheromones on its way back to the nest. Other workers follow that trail, reinforcing it each time they return with food. That is why a single ant on Monday can become a busy line by Wednesday, and why the same route gets used again and again.
Are black ants harmful?
Black garden ants do not bite or sting, and they are not known to carry disease in the way flies or rodents can. The problems are practical. They walk through dirt and rubbish outdoors before crossing worktops and getting into food, so anything they have been in should be thrown away. And a colony can be large, with many thousands of workers, so the numbers indoors can be hard to live with.
Finding the nest
The nest is the heart of the problem. To find it, watch where the ants go once they have picked up food. A little sugar on a piece of card placed near the trail makes this easier. Outdoors, look for fine piles of soil between paving slabs, along the edge of the lawn, in plant pots and at the foot of walls.
Nests are often close to the house, sometimes under a patio or path that butts against the wall. Occasionally ants nest in a gap in the brickwork or under a floor. A nest in a wall is harder to reach and is worth a professional look.
What you can do
- Remove the food. Wipe worktops after cooking, sweep under tables and around appliances, and wash up promptly. Keep sugar, cereals and sweet foods in sealed containers, and fruit in the fridge.
- Pick up pet food. Wash bowls after feeding and do not leave dry food down all day.
- Break the trail. Wash the route the ants are using with a detergent or vinegar solution. It removes the scent trail, but it will not stop ants laying a new one.
- Seal the way in. Fill cracks around door and window frames, along skirting boards and where pipes enter the house.
- Manage the outside. Keep bins lidded and away from doors, and trim back plants touching the walls.
Why sprays and boiling water often fail
Sprays and powders kill the ants they touch, which clears the worktop for a day or two. The queen keeps laying, so the workers are replaced and the trail starts again. Repellent products can also push ants to find a different route in.
Pouring boiling water into a nest kills the workers it reaches, but water cools quickly in soil. If it does not get deep enough to reach the queen and brood, the colony recovers.
Ant baits work differently: workers carry the bait back to feed the colony, including the queen. They can be effective, but they are slow and they fail if the bait is the wrong type for the ants, placed away from the trail, or competing with an easier food source. They should never be used alongside sprays on the same trail, which kill the workers before they can carry the bait home.
When to call us
If ants keep coming in after you have cleaned up and sealed the obvious gaps, if you cannot find the nest, or if they seem to be coming from inside a wall or floor, call us. We identify the ants, find where they are nesting and treat the colony, then show you where they are getting in. Our ant control page explains how we work.