Which ants are they?
Black garden ants (Lasius niger) are the ants most people see. They are dark brown to black, about 4 to 5 mm long, and nest outdoors under paving, in walls and in lawns. Workers come indoors following scent trails to sugary food. Pharaoh ants are tiny, about 2 mm, and pale yellow to light brown. They nest inside heated buildings, in wall voids and behind skirting, and are common in blocks of flats, hospitals and offices. They need specialist treatment, because sprays can make colonies split and spread.
Find the source
Watch the trail to see where the ants are coming from. Common entry points are gaps under back doors, cracks in floor tiles at the edge of the kitchen, gaps around pipes under the sink and expansion gaps behind units.
What you can do
- Wipe up crumbs and sugary spills and keep sweet foods in sealed containers
- Rinse recycling and keep bins closed
- Wipe the trail with soapy water or a surface cleaner to remove the scent
- Seal small cracks and gaps where ants enter
- Use ant bait stations along the trail, rather than sprays, so workers carry bait back to the nest
When to call a professional
If ants keep returning, if you see ants coming from inside walls or floors, or if you think you have Pharaoh ants, professional treatment targets the nest rather than the workers you can see. See ant control.
Questions and answers
Why do ants appear suddenly?
Scouts find food and leave a scent trail that hundreds of other workers follow.
Are ants harmful?
Garden ants are a nuisance rather than a health risk. Pharaoh ants can carry bacteria in hospitals and food areas.
Should I spray ants?
Sprays kill the ants you see but not the nest. Baits work better for most ant problems.
Related pages
This page is general information, last reviewed on 19 October 2026. It is not a substitute for an on-site inspection.