Ants in the house: where they come from and how to keep them out

Ants in the house almost always come from a nest outside. A few scouts find crumbs or sugar, lay a scent trail, and shortly afterwards a whole line of ants is marching through the kitchen. Break the trail and remove the food source, and you are already a long way there.

What attracts ants and where do they come from?

Sweet things such as sugar, syrup, honey and fruit, but also protein and fat. The nest is usually outside, under patio slabs, in the lawn or in the cavity wall. From there, scouts go looking for food. When they find some, they lay a scent trail that the other ants follow to carry the food back to the nest.

When are ants around?

From spring to autumn. In winter the nest is dormant. As soon as it warms up in spring, the queen starts laying eggs again, and in summer you see the most ants. In high summer the winged ants swarm out to found new nests.

How fast do ants multiply?

Very fast in spring and summer. The queen then lays eggs continuously, which become new workers within a few weeks. A black garden ant queen can live for many years and build up a large colony in that time.

What do ant eggs look like?

The real eggs are tiny, white and oval, about half a millimetre long, and stay deep inside the nest. What people usually take for ant eggs are the pupae: white to pale yellow capsules a few millimetres long that look like grains of rice. If you find them under a paving slab or in a flower pot, there is a nest there.

How many ants live in a nest?

In the black garden ant (Lasius niger), the most common ant in Western Europe, a nest already holds several thousand workers after one year. After ten years a colony can grow to around 100,000 ants. The ants you see in the kitchen are only a small part of them.

Are ants harmful or dangerous?

Usually not. Some species can nip or bite. Ants can, however, contaminate food, and large nests under patios and paths can make slabs sink.

How do you keep ants out?

1. Seal the entrances. Close gaps around doors, windows and skirting boards.
2. Clean thoroughly. Remove crumbs and sticky residue straight away; wiping with vinegar and water also erases the scent trail.
3. Remove scouts early. Vacuum up single ants or put them outside before a trail forms.
4. Store food properly. Keep sugar, honey and sweets in tightly closing containers.
5. Disturb the nest outside. Dig over a nest in the garden or flood it with water so the colony moves.

How does an ant bait work?

Ants share their food mouth to mouth. A worker that feeds on the bait carries it back to the nest and passes it on to other ants, the larvae and the queen. That is why a bait reaches the nest, not just the ants you can see.