The Texas A&M study on fire ants showed that a combination of soapy water (Dawn dish soap) and orange oil worked best, better than any of the poisons or baits, at killing fire ants. I have used this treatment successfully for years and it kills them in droves and they abandon that nest for a long while, sometimes they come back many moths later, sometimes not at all. I'm having a hard getting them out of the vegetable garden though and I wonder about the effect of the soap and orange oil residue in the garden. I assume it breaks down and washes out with watering but does anyone know if it has a deleterious effect on the plants?