Treatment
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. Spray 0.5m up the outside walls and 0.5m out from the walls. Liquid insecticides from garden centres and hardware stores are repellent to ants and ideal for use as barriers and have reduced toxicity to people and pets. Insecticide sprays can be toxic to fish and aquatic invertebrates, so take care not to contaminate ponds and waterways, read the label and follow directions.
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 more severe infestation may call for a more thorough treatment and involve spraying the outer perimeter of the block along fence lines to prevent the migration of ants into the treated area from neighbouring properties and open areas, such as lawns and paving can be treated in a grid pattern. Such treatments may be conducted by pest control professionals.
The following areas may 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.
Most management practices are conducted in summer and autumn when populations peak. At the time of treatment, ground surfaces should be dry. Avoid watering treated areas for at least 24 hours after treatment. Rainfall or watering of treated surfaces before this time will reduce the effectiveness of the treatment by dilution and through increased volatilisation of the insecticide.
Before spraying, children’s toys, clothes on the line and items such as pet food or drink containers should be removed from the area. People and pets should be excluded from the sprayed area until the treatment is thoroughly dry and spraying should only occur when wind conditions are calm.
DPIRD does not recommend insecticidal dusts or powders for the control of Argentine ants and the granular ant baits are not taken by this species, and are likewise not recommended. Sugar-based gel bait formulations from supermarkets, hardware stores or found online can help control smaller populations.
When spraying ants, note that only a small percentage of the population is outside the nest at any one time and therefore only a small number are controlled directly. Further deaths of ants occur as the food/water requirements of the colony increase and the ants are forced to forage while the insecticide residues remain at lethal levels. However, the ants’ ability to bounce back from a spray application is high, and sometimes a second treatment is required two to four weeks after the initial one.
Spot treatments of resurgent activity after these initial broad-scale treatments, as required, will substantially increase the period over which the ants are kept under control.
Spreading Argentine ants
Apart from the natural radial expansion of existing colonies, Argentine ants are spread unintentionally through transport by humans via a wide range of commodities, including soil, pot plants, foodstuff and garbage. Several plant nurseries in metropolitan and country areas could be infested with Argentine ants and present a risk of spread. Be sure to check that pot plants or any other plant material you may receive are free of ants.
If you are moving house and taking pot plants with you, or giving pot plants to friends, check that the pots are free of ants or treat the pots by immersing the pot for 30 seconds in a solution of one of the insecticides mentioned above, as per label recommendations.
Identification service
Correct identification of the pest ant is worthwhile before commencing any control procedures. There are pest ants that can be more easily controlled without spraying, based on advice appropriate to that species. A free identification and advisory service is provided by the Department of Primary Industries and Regional Development. To submit specimens for identification, stick about a dozen ants to a piece of paper with clear tape and enter your contact details on the paper. To ensure good biosecurity measures, ensure the ants are dead before sending off in the mail.