The most effective treatment is to use oil-based baits containing the active ingredient hydramethylnon. They are available under various trade names from a chemical retailer or hardware store. The ants collect the small particles and take them back to their numerous nests where complete control of the colony can be achieved.
These baits must be broadcast over the infested areas as per instructions on the product label. The baits should never be heaped around ant mounds as this not only increases the risk to non-target organisms but is far less effective in the control of big-headed ants. While expensive, a small 170g container is sufficient to treat a normal-sized urban block. The entire area should be treated as infestations exist in lawns and garden beds and can quickly re-invade treated areas if only a small area of obvious infestation has been treated. If the entire property is treated it may take two to three months or longer before it is re-colonised from untreated neighbouring properties.
Mechanical hand-held rotary or spinning-disc spreaders, designed to distribute small granules like fertiliser, are ideal for evenly applying the baits. It may be necessary to dilute the bait evenly with clean, dry sand to ensure that the application rate is sufficiently low to allow coverage of the entire area. If using a fertiliser spreader, ensure it is clean so that the bait is not tainted with fertiliser residue which might stop the ants collecting the bait and taking it back to the nest.
Keep the bait in a cool, dry location when not in use. Since the bait attractant is oil, the bait can become rancid and unattractive to the ants if it is not stored correctly.
Bait should be broadcast when the ants are most active – this varies with the season:
- Hot weather in summer — apply the baits before 9am or after 4pm.
- Cold weather in winter— apply baits between 10am and 3pm.
Baits should remain dry for 12 hours after being applied. Therefore, do not apply if rain is expected and ensure irrigation does not come on within 12 hours of application.
Correct application of bait outside the building will also cure indoor ant infestations but do not apply the bait inside the home.
Protection of pets and wildlife
When applied correctly (broadcast) the baits should not present a risk to pets and birds. The bait should not be applied directly inside bird cages, and they can be toxic to fish and aquatic invertebrates, so take care not to contaminate ponds and waterways.