Diatomaceous Earth! Since I started using it, I haven't had any major ant outbreaks but prior to finding out about it, I'd have horrible outbreaks every July with several types of ants. I live in the desert and by July, they were all pretty desperate for water. It also kills the scorpions and cockroaches and fleas. Really, it's just a great all-purpose bug-killer that is environmentally friendly and safe for pets. Wherever you get it from, make sure that it is food-grade.