One of the most common ant species found in Australia is the Argentine Ant, Linepithema humile, which enters buildings in search of food and moisture.
Identifying an Argerntine Ant:
Argentine ants are very ordinary-looking, small brown ants. They are small and slender, 2.6 to 3.2mm long, and are dark brown in colour. The worker ants are uniform in shape and size and move in well defined trails.
As the name suggests, argentine ants originate from South America and were first recorded in Western Australia (WA) in 1941 — initially in Albany and then in Perth as well as many country locations across the state.
Their food preference is the sugary honeydew produced by aphids, mealy bugs and scale insects. Heavy trails of argentine ants are often seen on the trunks of trees and shrubs. This is economically significant in horticulture as it encourages heavy populations of these plant pests to develop. Argentine ants feed on a wide variety of foods, including sweet drinks, cakes, pet food, meat and dead insects. The queens can live for several years, and compared to other ant species, individual workers are long-lived too, surviving for 10 to 12 months. These features contribute to argentine ant infestations maintaining high populations.
Symptoms of infestation
Continuous well-defined trails, sometimes more than three ants wide, of slow-moving, small brown ants of uniform size are often evidence of an argentine ant infestation. The ants will often readily climb onto a person’s hand when it is placed in their trail. Many other ant species will not do this.
Argentine ants are typically confined to urban areas and they nest outside buildings, at the base of trees or in the tree itself, along the edges of paths and in lawns and garden beds. They will thrive in swamps and low-lying areas where moisture is plentiful.
Populations peak from January to June, and they can be very invasive, coming indoors in large numbers in their search for food and moisture.
Argentine ants remain the most difficult common pest ant in WA to control. Once cleared from an area, argentine ants can quickly re-colonise it from untreated neighbouring properties. This can occur within two weeks.
Argentine ants nest outdoors, but if ants are foraging inside the building there are two broad strategies to keep them outside.
Physical exclusion: Sealing the cracks and crevices through which they are entering. Argentine ants are resourceful, however, and are likely to find alternative routes which will require similar treatment.
Chemical exclusion: An insecticide barrier can be sprayed around the entire outside perimeter of the house, including doorways and window sills.
Attention needs to be paid to situations which could allow the ants to bypass the barrier, for example, foliage in contact with the building or additions to the building like patios and pergolas which could provide an alternative route.
A thorough treatment will involve spraying the outer perimeter of the block along fence lines to prevent the migration of ants into the treated area from neighbouring properties. Then spray around the outer perimeter of the building for half a metre up the foundations/walls and half a metre out from the foundations.
The following areas also require treatment:
all nests and ant trails
edges of paths and driveways
garden beds adjacent to the building
butts of all trees and large shrubs
areas around rubbish bins and taps, to isolate the ants from these food/water sources.
Source: Department of Agriculture & Food of Western Australia
Professional pest control
A qualified and licensed pest control operator can determine the type, source and extent of the infestation and use registered insecticides to control ant infestations. Good hygiene practices, such as frequent house cleaning, should reduce the risk of further infestations.