Non-toxic options are preferred by people who wish to avoid the potential risk of non-target effects altogether.
Often these options require more effort, but they are cost effective.
Hot water can be used to kill entire colonies of fire ants if a large enough volume of hot water is applied directly to the mound (using a large kettle for example). Water temperature should be above 65°C (and ideally above 82°C) to be lethal to the ants. The volume of water applied will depend upon the size of the nest. For very small colonies 4 L of water may be sufficient. For larger colonies as much as 75 L of hot water may be necessary to reach the below-ground nest structure and kill all of the ants. Water can be applied by pouring into the mound after opening the above ground structure with a long stick or rod to assure that the water flows below-ground and does not just wash away the mound on the ground surface. Alternatively, water can be injected below-ground if a hollow wand or tube is available to deliver the water.
It is important to note that all control methods require regular site visits and application of the control method as the presence of fire ants throughout the landscape assures that sites left untreated will be recolonized. Hot water treatment, if delivered below-ground, at high enough temperature, and sufficient volume, will be immediately lethal but nests should be rechecked for activity and retreated after the initial treatment (within 2-3 weeks) if additional activity is detected. For control of individual mounds, hot water treatments offer a rapid, entirely non-toxic alternative for problem mounds.
Information was provided by Josh King, University of Central Florida, firstname.lastname@example.org
Technology transfer UCF, Simple solution for exterminating fire ants
Salt water dousing
Salt water dousing involves looking for the ant nest and destroying it (i.e. targeted treatment of nests with salt water dousing).
The idea is to follow foragers back to the nest entrance and flood the nest with salt water.
This forces the queens out of the nest. It is important to to stay and wait for the queens to leave and kill them directly. Queens are very good at escaping and hiding so you need to look carefully. The nest and surrounding area needs to be checked over the following few days and re-treated if necessary.
Note that if the nest isn't effectively destroyed remaining queens and workers can leave the colony by budding.
This is a very labour intensive method, but an option if there aren't any others.
Keeping things clean
|The number one thing you can do to make ant problems less painful is to remove resources e.g. nesting materials, food scraps, treatment of the plant pests that are helpful to ants.
Sometimes wiping the ants away with a damp cloth can get rid of ants that are foraging (e.g. in kitchens).
If you wipe away any ants that you see for a few days they should stop coming in.
This probably works because other ants notice the smells of their dead nestmates and / or it disrupts their foraging trails.
Either way the ants realise the area is not safe. Yes, ants are that smart!
Rubbish piles provide a fantastic source of food and nesting locations for invasive ants (© Monica Gruber, Pacific Biosecurity)
A note about boric acid based treatments
Treatments using boric acid are often called non-toxic. However, the boric acid can accumulate in the environment and have non-target effects.
Wikihow has information on spraying / wiping with vinegar / lemon juice solutions, soapy water.