About this guide
Ants in the house in the UK are usually black garden ants entering in summer while foraging — a seasonal nuisance rather than a persistent infestation. In some heated buildings, particularly flats and houses with underfloor heating, pharaoh ants are the cause — and these require completely different treatment. This guide explains why ants come inside, how to identify which species is present, what works to get rid of them, and what to do about flying ants inside the house.
Why Ants Come Into Houses
Black garden ants (Lasius niger) enter houses primarily for food — they are foraging for carbohydrates (sugary substances, honeydew, sweet food scraps) and protein. Ant foraging is intensified in hot, dry summer weather when the soil moisture that maintains aphid colonies — the ants' primary outdoor food source of honeydew — declines. When outdoor foraging becomes less productive, scout ants explore adjacent structures (houses, outbuildings, garages) for food. A scout that finds a food source inside a house deposits a pheromone trail on the return journey to the nest — subsequent workers follow the trail, reinforcing it with their own pheromone deposits, creating the visible foraging trail lines that homeowners find on kitchen worktops, floors and around food storage.
This foraging behaviour explains why wiping away ant trails and killing the visible ants does not solve the problem. The nest is outside — usually in the garden, under the path or beneath the building foundation — and will continue to produce foraging workers as long as the food source is available or the scout trail persists. The solution is to either remove the food source entirely, treat the nest, or treat the entry routes with a residual product that kills foraging workers before they establish a productive trail.
How Ants Get In — Common Entry Routes
Ants enter houses through small gaps that are straightforward for a 3–5 mm insect to exploit: gaps under external doors and around door frames (particularly where the threshold seal has worn); gaps around water and gas pipes, cables and ducting entering through external walls or floors; cracks in rendered external walls; gaps in the mortar between the bottom course of brickwork and the floor; gaps around skirting boards where these adjoin external walls; and, in older properties, through air brick ventilation openings that connect to sub-floor voids. Identifying the active entry route and treating it directly — as part of a nest treatment programme — is more effective than trying to treat individual ants throughout the interior.
Ants Under the Kitchen Floor
A very common scenario in UK houses is garden ants nesting beneath the kitchen floor — under the concrete slab or within the floor screed — with access to the kitchen via the gap around the base of kitchen units, under the kickboard, or through cracks in the floor covering. These nests are difficult to treat without professional access because the nest is inaccessible from outside (being directly beneath the building) and interior spraying does not penetrate to the queen. A professional technician can treat through drill holes in the kickboard or floor area with appropriately formulated insecticide, or use a bait programme that workers carry into the nest from accessible interior locations.
Pharaoh Ants in Houses — A Different Problem Entirely
If you have ants indoors year-round — including in winter — and they are very small (1.5–2 mm), pale yellow or orange, and appear to be nesting inside the fabric of the building rather than entering from outside, pharaoh ants (Monomorium pharaonis) are a strong possibility. Pharaoh ants are a tropical species that cannot survive in UK outdoor conditions — they are exclusively indoor pests, dependent on the warmth of heated buildings. They nest in cavities within walls, under floors, in insulation and in electrical conduit. Unlike garden ants, pharaoh ants are active year-round, do not swarm, and are present as a continuous indoor infestation rather than a seasonal incursion.
The critical rule with pharaoh ants: do not apply any residual insecticide spray anywhere in the building. This triggers budding — the colony survives the chemical stress by fragmenting into multiple sub-colonies that disperse through the building, establishing new nesting sites in locations not yet reached by the spray. The infestation becomes more widespread and harder to treat with each spraying event. Pharaoh ant management requires a professional slow-acting bait programme with no residual pesticide use — this is not a DIY task. The programme takes 8–12 weeks minimum and must be managed by a qualified pest controller experienced in pharaoh ant management.
Pharaoh ants (Monomorium pharaonis) in UK hospitals have been associated with wound and burn infection incidents — workers enter dressings and food sources, carrying bacteria including Enterobacter cloacae and Pseudomonas aeruginosa. In healthcare settings, pharaoh ant infestation requires urgent professional bait treatment.
— Published medical and public health literature; HSE
Getting Rid of Garden Ants in the House — Treatment Options
For garden ants (the black ants seen in trails in summer), the most effective approaches are: locating and treating the nest directly, where it is accessible in the garden; treating the entry point(s) with a residual contact insecticide that kills incoming foragers; and using slow-acting bait products that workers carry back to the nest and feed to the queen and brood.
Residual contact spray (deltamethrin, cypermethrin or lambda-cyhalothrin) applied to entry points and trails kills incoming foragers and disrupts the pheromone trail. This reduces interior ant activity quickly but is not a long-term solution if the nest remains active and accessible entry points are not sealed. Slow-acting gel bait products placed at active trailing locations — not sprayed over, which would deter workers from the bait — are taken back to the colony by foraging workers and fed to the queen and larvae. This is the most effective approach for achieving lasting colony reduction. DIY gel bait products are available from hardware stores and can be effective if used correctly: small amounts at trailing locations, not disturbed, replaced regularly.
Flying Ants in the House
Flying ants indoors — in July or August, often after a period of warm humid weather — are winged reproductives (alates) from a garden ant colony. These are virgin queens and male ants leaving the nest to mate during the annual nuptial flight. Finding flying ants indoors usually means there is a nest in or adjacent to the building, or that flying ants from garden nests have found their way inside through open windows or unsealed gaps. Flying ants do not nest indoors — the queens that land and shed their wings go on to found new nests outside. The event is temporary (typically 1–3 days), after which ant activity indoors ceases. Sealing gaps around doors and windows before the nuptial flight period reduces the number entering the house. Vacuuming up flying ants that do enter is the simplest immediate response.
Food Hygiene Is the Most Important Ant Prevention Measure — Ants enter houses to find food. The most effective long-term prevention is removing the food source that is attracting them: store all food in sealed containers or the refrigerator, clean up spills and crumbs immediately, empty and clean pet food bowls after feeding, empty food waste bins daily and clean the bin regularly, and ensure compost bins are sealed. Ants that find no food source in a house will cease to forage there — they follow productive trails. Removing the reward removes the incentive, even if the nest remains in the garden.
When DIY Is Not Enough — Calling a Professional
Call a professional ant pest controller if: ants are present year-round inside the house (possible pharaoh ants — do not spray); DIY treatment has been applied repeatedly without lasting effect; ants are nesting inside the building fabric rather than entering from outside; the ant trail source is under the floor or within inaccessible voids; there is ant activity in a kitchen or food storage area in a food business; or the property is a rental where the infestation is the landlord's responsibility to address. In Leeds and Sheffield, Apex Pest Control Ltd provides ant species identification and targeted treatment using professional-grade residual insecticides and bait programmes for all residential and commercial ant situations.
Frequently Asked Questions
Why do I suddenly have ants in my kitchen?
A sudden appearance of ants in the kitchen is typically black garden ants foraging for food from a nest in the garden or beneath the building. Scout ants find a food source — crumbs, a spill, a food container with residue — and deposit a pheromone trail that other workers follow, creating the visible column of ants. This happens most commonly in July and August when hot dry conditions deplete aphid honeydew in the garden, making indoor food sources more attractive.
The nest is outside — the ants you see in the kitchen are foragers, not residents. Removing the food source and treating the trail and entry point disrupts the foraging activity quickly.
Do ants nest inside houses?
Black garden ants do not normally establish permanent nests inside house walls or structures — they nest in soil outside and forage inside for food. However, they can nest under kitchen floors, beneath concrete slabs, within sub-floor voids, and in garden beds immediately adjacent to the building. In these cases, the nest is physically very close to or beneath the building, making interior ant activity feel like an interior infestation.
Pharaoh ants do nest inside building fabric — within wall cavities, under flooring, in roof insulation, in electrical conduit and in heated floor systems. Year-round indoor ant activity that intensifies in winter (when garden ants are dormant) indicates pharaoh ants.
What kills ants instantly in the house?
Contact insecticide sprays (deltamethrin, cypermethrin, lambda-cyhalothrin) kill ants immediately on contact and provide a residual barrier on treated surfaces. They are effective at reducing visible ant numbers quickly. However, instant kill of workers does not affect the nest — the colony produces new foragers continuously.
For a lasting result, slow-acting bait is more effective than contact spray, as it is carried back to the nest and fed to the queen and brood. Boiling water poured directly onto an accessible nest entrance provides rapid knockdown of surface nest activity. In all cases, the goal should be nest elimination or significant colony reduction, not just killing the visible workers.
Is it normal to have ants in the house in summer?
Yes — seasonal garden ant entry into houses in June to August is very common in UK properties with gardens. It is a nuisance problem, not a sign of structural infestation or a serious health risk in a domestic setting. The most common scenario is a trail of black ants appearing in the kitchen for a few days following hot weather, usually from a gap under the back door, around pipes under the sink, or along the skirting board at an external wall.
Good food hygiene (removing the food source), sealing the entry gap, and applying a gel bait at the trailing location typically resolves the issue within a week. If ant activity continues beyond 2–3 weeks despite these measures, a professional treatment is worthwhile.
How do I get rid of ants without using chemicals?
Non-chemical approaches to house ant control include: removing all accessible food sources (sealed containers, cleaned surfaces, lifted pet food bowls); blocking entry routes with exterior-grade sealant around gaps under doors, around pipes, and at skirting board junctions with external walls; disrupting pheromone trails by cleaning them with white vinegar or soapy water (this removes the chemical signal temporarily); applying diatomaceous earth at entry points (desiccates ants on contact — limited practical effectiveness outdoors but can work at interior entry points in dry conditions); and applying a physical deterrent such as cinnamon powder or coffee grounds at entry points (anecdotal, not scientifically validated). For persistent infestations where the nest must be eliminated, chemical treatment is the only reliable method.
Why are there ants in my bathroom?
Ants in the bathroom are usually foraging for water — ants need moisture as well as food, and during dry summer periods the bathroom provides accessible water sources (condensation, dripping taps, the area under the bath or around the basin). The entry route is typically through gaps around pipework entering through the wall or floor. Checking for and sealing gaps around bath and basin pipes, fixing any dripping fittings, and ensuring the bathroom is well ventilated (reducing condensation) removes the water source.
A very small number of ants in the bathroom are usually scouts and should cease within a few days if the moisture source is removed. Persistent bathroom ant activity despite moisture control suggests a nest under the bathroom floor — professional treatment may be needed.
Can my landlord be required to deal with ants in a rented property?
Under the Landlord and Tenant Act 1985 and the Housing Act 2004, landlords are responsible for maintaining rental properties in a habitable condition, which includes pest management where the infestation arises from a structural defect (gaps in building fabric, poor-condition doors, cracked foundation walls allowing ant access). If ants are entering the property through structural defects, this is the landlord's responsibility to address. If ant activity is related to tenant food hygiene practices, it may be considered a tenant responsibility.
In practice, most ant infestations involve both factors — the building has accessible entry routes and there is food available inside. Tenants should report ant infestations to their landlord in writing and request treatment; if the landlord fails to respond, the local authority environmental health department may assist.
Get Rid of Ants in Your House — West and South Yorkshire
Apex Pest Control Ltd treats ants in houses across Leeds, Sheffield, Barnsley and Rotherham — from seasonal garden ant entry to professional pharaoh ant bait programmes. Call us for a same-season treatment that targets the nest, not just the foraging trail.
Contact Apex Pest Control Ltd for ant treatment.