find the nests and if they are in the ground away from the house pour petrol (gasoline) in the hole and remove the can well away from the area and strike a match and throw it on the petrol soaked ground. Dig down a bit after the initial flames have died down and that will allow air to get down further. I use this method to get rid of an agressive ant called a jackjumper that causes very bad alergic reactions and even death here. Mylate dad had to have an injection of adrenilin nearby as the anaphylatic reaction when bitten nearly killed him twice.

Borax powder that the ants carry back to there nest is very effective too but not nearly as much fun as burning the bastards LOL