Ants invade our homes in search of sweetness


Ants are commonly found in Ireland and frequently in proximity to human dwellings. The two species of concern are the Black Garden Ant (Lasius niger) and Pharaoh’s Ant (Monomorium pharaonis). Black ants nest in the soil under sun-warmed paved areas and are particularly attracted to sweetness – honeydew (aphid secretions), fruit and caterpillars. They guard aphids that damage garden plants and flying ants may emerge in large numbers close to or inside houses.


Pharaoh’s ants are found only in heated buildings nesting in cavities and heating ducts. Common with all the species of the order Hymenoptera (bees, wasps & ants) follows a complete metamorphosis lifecycle in about 1-2 weeks with a 10-12 weeks life span. Black ants only have one queen, but Pharaoh’s colonies have several queens all of which lay eggs. Workers will move pupae and young larvae away if danger threatens the nest. A minimum breeding temperature of around 18°C with an optimum of 30°C.


Pharaoh’s worker ants are most commonly encounteredin buildings with central heating systems, ovens, comms rooms, hotels, food manufacturing, sometimes heat exchange units (calorifiers) in institutions such as hospitals, nursing homes, prisons and increasingly high-rise apartments. Worker ants communicate with other ants using a trail of pheromones to inform other ants there is a food source. The ants also search out liquid water for drinking and this is often brings them into contact with unsavoury areas such as drains and waste-food collection bins.


Pharaohs ants are 2mm long and yellowish in colour. Nest sites are often difficult to find, and a visual survey does not easily detail the extent of the infestation. Due to being small they can contaminate packaging by entering otherwise sealed containers often entering sterile hospital supplies and foodstuffs. They spread Salmonella, Staphylococcus and E coli. Particularly attracted to wounds of patients in hospitals or nursing homes causing intense irritation and the prospect of the transmission of pathogenic bacteria.


Pharaohs are difficult to eradicate despite best efforts to control. Garden ants should be controlled by sealing obvious faults in building structures with mortar or mastic. Residual sprays and dusts are usually ineffective in eradicating Pharaoh’s as insecticide within a range will induce migration away from a treated area, encouraging spread of the infestation. The worker ant’s ability to “bud-off” new colonies if subjected to unusual stressors frequently results in many smaller satellite colonies spreading easily from building to building.


Professional products formulated with an attractant bait base as ready to use bait stations should achieve control within 12-14 weeks if used correctly. While treatments do not have an immediate effect, a baiting strategy is most effective. In sensitive areas e.g., hospital wards or operating theatres where worker ants are reduced quickly a treatment of a residual insecticide at 10-14 days only after completion of a baiting treatment. Disruption to a colony structure will only result in the nest being moved to a new location.


Call us for a site survey (086) 812 0435.

Mervyn WalshBA(Hons), HDip.EnvMgt, MRSPH

Field Conservation Biologist