Ants indoors: identify the species, target the nest
The trail on your worktop is only the visible part of a hidden colony.
The short answer
Two ants cause most problems in buildings: the black garden ant (Lasius niger), which nests outdoors and comes in during spring and summer, and the pharaoh ant (Monomorium pharaonis), tiny and pale yellow, which lives inside heated buildings. The workers you see are only a small part of the colony: a slow-acting bait carried back to the nest is how the queens are reached.
Identity card
Scientific name: Lasius niger, Monomorium pharaonis
- Size
- 3–5 mm for a black garden ant worker; about 2 mm for the pharaoh ant
- Appearance
- Black ant: very dark brown to black; pharaoh ant: pale yellow to amber, darker abdomen
- Life expectancy
- A few weeks to a few months for a worker; several years for a black garden ant queen
- Active period
- Black ant: spring to autumn; pharaoh ant: all year round in heated buildings
- Where it hides
- Worktops, thresholds, skirting boards, tile joints, paving and planters, service ducts
How to spot ants
Tick off in your head what you have seen: the more the clues overlap, the surer the diagnosis.
- Steady trails between a crack (threshold, skirting, socket) and a source of sugar, fat or water.
- Small mounds of fine soil between patio slabs or at the foot of walls.
- A mass emergence of winged ants from a crack on a hot, muggy summer day.
- Tiny yellowish ants near water, in the bathroom or around sockets: most likely the pharaoh ant.
Understanding how it behaves
A worker that finds sugar or fat marks its way home with a scent trail that others follow: that is how a trail forms. Squashing ants or wiping the trail does nothing to the nest, which simply sends out new workers.
Knowing the species changes everything. The black garden ant builds its nest under a paving slab, at the foot of a wall or in a planter. The pharaoh ant nests in wall linings, ducts and behind skirting boards, with many queens; a repellent insecticide can push its colony to split into several new nests.
In commercial kitchens, healthcare settings and food shops, the pharaoh ant is taken seriously: it moves throughout the building, sensitive areas included.
Why it shouldn't be left
- Food, worktops and pet bowls soiled.
- Pharaoh ant: possible transfer of germs from one part of a building to another, a concern in catering kitchens and care facilities.
- A nuisance that returns every season as long as the colony and its queens survive.
- A swarm of winged ants indoors for a few hours, an unsettling sight.
What the technician does: ants
01
Inspect
Species identification, trails followed back to entry points, search for likely nests indoors and out.
02
Treat
Slow-acting gel or bait placed on the trails, which workers carry back and share all the way to the queens; no repellent spraying nearby.
03
Sanitise
Sealant on thresholds, skirting boards and duct openings, advice on storing food and cleaning trails once the bait has been taken.
04
Follow up
Follow-up visit as set out in the protocol, bait renewed if activity continues, photo report and active vigilance as spring approaches.
Prevention, at home and at work
Simple habits that lower the risk of the intruder settling in or coming back.
- 01At home: wipe up spilt sugar, honey, juice and jam straight away.
- 02Keep sugar, biscuits and pet food in containers that close tightly.
- 03Cut back branches and climbing plants that touch the walls or window sills.
- 04Don't spray insecticide near a bait: the ants would avoid it.
- 05In a business: check stockrooms and storage areas in spring, and report any pale yellow ants seen indoors.
Your questions
They come back every year: what does that mean?
That the colony, often outdoors, has survived the winter. As long as the queens are alive, new workers find the same way in as soon as the weather warms up.
Do home remedies (vinegar, lemon, chalk) do anything?
They scramble the scent trail for a few hours or days without touching the nest. The workers soon find another route.
Why are there more ants right after the bait goes down?
It is usually a good sign: workers gather to carry it back to the nest. Leave them to it and don't wipe the bait away; activity generally falls after a few days to two weeks.
When should I call in a professional?
If the ants keep returning despite your precautions, if you suspect pharaoh ants or if you run a food business. The technician identifies the species and chooses the right bait.
Ants at home or on your premises?
2-hour slot, 7 days a week from 8 am to 8 pm, price shown and paid online, photo report emailed on the day of the visit.
Related service: Crawling insect treatment
