About this guide
Garden ants are a natural and largely beneficial part of the UK garden ecosystem — they aerate soil, decompose organic matter and predate on pest insects. The question of whether to treat garden ants is really about whether the colony is causing specific damage to your property (lifting paving, damaging a lawn) or creating a genuine problem by entering the house repeatedly. This guide covers the property damage garden ants can cause, the nest treatment methods that actually work, what DIY products achieve, and when ants in the garden warrant professional treatment.
Are Garden Ants Actually a Problem?
Black garden ants (Lasius niger) are one of the most common insects in UK gardens and are broadly beneficial in the garden ecosystem. They aerate soil as they excavate nest galleries, break down organic matter, and predate on pest insects including aphid eggs and small caterpillars. A garden with an established ant colony is not automatically a garden with a pest problem — it is a normal, ecologically functioning garden. The decision to treat ants in a garden should be based on whether the colony is causing specific, identifiable damage or disruption: lifting paving slabs, creating mounds in a lawn or bowling green, repeatedly entering the house in large numbers, or causing crop damage in a food growing area.
Ant colonies in gardens are not easy to permanently eliminate — they are deeply established in the soil, queens can live for 15 years or more, and new colonies from nuptial flights can establish in treated areas. Treatment targets the current problem rather than creating a permanently ant-free garden, which is not a realistic or particularly desirable objective in most cases.
Damage Garden Ants Cause to Garden Structures
The main physical damage garden ants cause to property falls into two categories: paving and path instability, and lawn damage.
Ants Under Paving
Garden ants nesting beneath paving slabs, path edges and block paving excavate the sand or mortar bedding layer to create nest galleries — removing material from the substrate and creating voids beneath the surface. This causes individual slabs to become unstable, rock or tilt, and — in path or driveway applications — creates trip hazards and uneven surfaces. The characteristic sign is fine sandy or granular material pushed up through the joints between slabs, forming small mounds at the edges. Treating a nest beneath paving requires either treating through the joints with a residual liquid insecticide or a nest drench (diluted insecticide poured down into the joint gap to penetrate the nest structure), or lifting the affected slabs temporarily to gain access to the nest and rebedding after treatment. Where paving damage is extensive, professional treatment and rebed of the affected area may be warranted.
Ant Mounds in Lawns
In established garden lawns, ant nests create mounds of fine, loosened soil at the surface — the result of nest excavation activity bringing material upward. In bowling greens, sports turf, croquet lawns and high-quality ornamental lawns, ant mounds are a significant surface quality problem: they disrupt the turf surface, create bare patches where grass is excluded by the mound material, and — when the mounds are flattened by mowing — smear fine soil across the grass, creating poor surface conditions. On domestic lawns, a degree of ant activity is normal and not necessarily requiring treatment. Where mounds are extensive and disrupting turf quality, a nest drench programme targeting the visible mounds directly is the most effective approach.
Nest Treatment Methods
For garden ant nests that are causing specific problems, the available treatment options are nest drenching, residual spray to nest entrance and foraging trails, slow-acting bait products, and — as a temporary disruptive measure — boiling water.
Nest Drenching
Nest drenching involves pouring a diluted insecticide solution directly into the nest entrance and, where accessible, into the nest galleries — with sufficient volume to penetrate deep into the nest structure and contact the queen and brood. Professional nest drenching uses approved formulations (typically synthetic pyrethroid or organophosphate products registered for this use) at the correct dilution, applied with sufficient volume (typically 5–10 litres per nest depending on size) to achieve penetration. A correctly executed nest drench is the most rapidly effective method — it kills the queen and brood directly and eliminates the colony within 24–72 hours. The challenge is ensuring the liquid actually reaches the deep nest chambers: an ant mound may extend 30–60 cm below the surface, and a surface application alone may not penetrate adequately.
Residual Spray and Bait
Residual contact spray applied to the nest entrance, foraging trails and building entry points kills workers and disrupts the trail pheromone network — this reduces foraging activity from that nest into the house or across a treated surface. It does not reach the queen or deep brood chambers and will not eliminate the colony. Slow-acting bait products (gel or granular) placed at active trailing locations are taken back to the nest by foraging workers and fed to the queen and larvae — this is the most effective non-professional method for achieving colony suppression over a 2–4 week period. Bait must not be placed on or adjacent to areas treated with insecticide spray, as contamination makes the bait unacceptable to workers.
A black garden ant colony typically contains 5,000–15,000 workers and is supported by a single queen that can live for 15 years or more. Garden ant nests may extend 30–60 cm below the soil surface — shallow surface treatments rarely penetrate to the queen and brood.
— Entomological research; BPCA species guidance
Boiling Water
Pouring boiling water into the nest entrance is a commonly described home remedy. It kills ants in the surface layers of the nest but is rarely effective against a deep, well-established colony — the water cools rapidly as it percolates through soil and does not maintain a lethal temperature at depth. It is most effective against small, shallow nests in the early part of the season before the colony is fully established. Boiling water applied repeatedly over several days may reduce surface ant activity and disrupt the nest enough to cause the colony to relocate, but it does not reliably kill the queen. It also risks damaging nearby plant roots if applied in planted areas.
Flying Ants in the Garden Are a Natural Seasonal Event — The mass emergence of winged ants — flying ant day — typically in July or August in warm humid conditions — is a natural nuptial flight event, not an invasion. Winged ants (alates) are virgin queens and males leaving the nest to mate. Birds eat them in large quantities. The event lasts 1–3 days and then ceases naturally. It does not indicate a worsening ant problem — it is a normal part of the garden ant lifecycle. No treatment of flying ants in the garden is either necessary or effective.
Ants and Garden Plants
Garden ants farm aphids — tending aphid colonies on plant stems, protecting aphids from predators, and harvesting their honeydew secretions as a food source. This aphid-farming relationship can contribute to plant damage from aphid feeding, as the ants remove natural predators (ladybirds, lacewing larvae) that would otherwise keep aphid populations in check. If a garden plant is suffering from a persistent aphid infestation accompanied by heavy ant activity, treating the ant trails on the plant stem with a sticky barrier (proprietary ant grease bands for trees and shrubs, or tape with a suitable deterrent) physically prevents ants from reaching the aphid colony without using insecticide — this allows natural predators to suppress the aphid population over time.
When Professional Garden Ant Treatment Is Warranted
Most garden ant problems do not require professional pest control — they can be managed with appropriate DIY products, food hygiene measures inside the house, and targeted nest treatment when needed. Professional treatment is appropriate where: ants are nesting under building foundations and entering the house persistently (with the nest not accessible from the garden); ant mounds on a commercial sports surface, croquet lawn or high-value ornamental area require professional treatment for surface quality reasons; a large number of nests in a garden or grounds are causing extensive paving or structure damage; or the ant species involved may be pharaoh ants or another species requiring professional identification. In Leeds and Sheffield, Apex Pest Control Ltd provides nest location, species identification and targeted treatment for garden and property ant problems across West and South Yorkshire.
Frequently Asked Questions
Should I get rid of garden ants?
Garden ants are part of a healthy garden ecosystem and control is not always necessary. Ants aerate soil, help decompose organic material and predate on some pest insects. Control is appropriate when ants are causing specific problems: nesting under paving and causing structural instability; creating extensive mounds in a lawn or sports turf; farming aphid colonies on plants you want to protect; or repeatedly entering the house in numbers that conventional hygiene measures cannot control.
If ants in the garden are not causing any of these specific problems, leaving them undisturbed is a reasonable ecological choice and will make no practical difference to the garden.
What is the best way to kill a garden ant nest?
The most effective method for eliminating a garden ant nest is professional nest drenching with a diluted insecticide solution in sufficient volume to penetrate to the queen and deep brood chambers — typically 5–10 litres per substantial nest, applied through the nest entrance and into galleries where accessible. For a DIY approach, ant nest killer powder or diluted liquid insecticide products designed for nest drenching (deltamethrin or permethrin-based products available from garden centres) applied directly to the nest entrance and, where possible, excavated into the nest entrance channel, are more effective than surface spraying. Slow-acting bait granules scattered around the nest entrance are carried inside by workers and fed to the queen — these take longer (2–4 weeks) but can achieve colony elimination without direct access to the nest.
How do I stop ants from lifting my paving?
To prevent ants nesting under paving: treat existing nests in or adjacent to the paving area with nest drench before re-sanding; use kiln-dried polymeric jointing sand (rather than standard builders sand) when bedding and jointing block paving or slab paths — polymeric sand sets hard in the joints and is more resistant to ant excavation; ensure the sub-base is well-compacted and adequately deep (ants prefer loose, friable substrate). Treating the perimeter of paved areas with a residual insecticide at the start of the active season can reduce new colony establishment. Where an established nest has caused significant substrate excavation and surface instability, lifting and resetting the affected slabs over re-compacted sand is the correct repair approach, carried out after the nest has been treated.
Can I pour boiling water on an ant nest?
Boiling water poured into an ant nest entrance kills workers in the surface layers of the nest and disrupts the upper gallery structure. It is most effective against small, shallow nests in the early season. Its limitations are significant: the water cools rapidly as it moves through soil and rarely reaches the queen in a mature, deep nest at lethal temperature; garden ant nests extend 30–60 cm below the surface; and in planted areas, boiling water kills plant roots in the treatment zone.
It may cause the colony to relocate rather than eliminating it. For a well-established nest, a purpose-designed insecticide nest drench in sufficient volume and concentration is substantially more reliable than boiling water.
Will ant killer harm my garden plants?
Residual contact insecticides applied directly to plant stems or leaves can cause phytotoxicity — leaf scorch or damage — particularly on delicate plants or in hot sunny conditions. Most garden ant treatment should be targeted at the nest entrance and soil around it, or at building entry points, rather than applied across plants. Slow-acting bait granules placed at the nest entrance or along trails at soil level have minimal risk to plants when used as directed.
Avoid applying liquid insecticide during flowering periods when pollinators (including bees) may contact treated surfaces. Where ants are farming aphids on specific plants, a physical barrier (sticky grease band on the stem below the aphid colony) disrupts the ant-aphid relationship without using insecticide on the plant at all.
Do ants damage grass and lawns?
Garden ant nesting in lawns creates mounds of fine soil at the surface — the result of excavation bringing subsoil material upward. In domestic lawns, a degree of mounding is cosmetically noticeable but rarely causes serious turf damage. In sports turf, bowling greens and high-quality ornamental lawns, ant mounds significantly disrupt surface levels and playing quality.
The mounds themselves do not kill grass — the turf surface is displaced and weakened around each mound, creating bare patches. Treatment involves applying a nest drench or professional residual insecticide directly to the mound sites and allowing the material to penetrate; the mounds can be lightly raked into the lawn after treatment once the colony is no longer active, restoring surface levels.
Are flying ants in the garden dangerous?
Flying ants — the annual nuptial flight of winged garden ant reproductives — are not dangerous. They do not sting and are not aggressive. The event involves large numbers of winged males and virgin queens leaving established nests simultaneously (usually in July or August, triggered by warm humid weather after rain), mating in flight, and dispersing.
The males die within days; fertilised queens shed their wings and attempt to found new colonies. Flying ants are eaten in large quantities by swifts, swallows and gulls. Flying ant day is a natural ecological event and is not something that warrants treatment.
If flying ants are entering the house in large numbers through open windows or gaps, temporarily closing affected windows for the 1–3 days of peak nuptial flight activity is the practical response.
Ant Control in Gardens Across West and South Yorkshire
Apex Pest Control Ltd treats persistent garden ant infestations across Leeds, Sheffield, Barnsley and Rotherham — nest drenching, residual treatments to entry points, and professional bait programmes where nests are inaccessible. Contact us for garden and property ant control.
Contact Apex Pest Control Ltd for a garden ant assessment.