Today's thrify tip is to use instant grits to kill black ant hills. This really does work. The theory is that the grits are eaten which then will expand in the belly killing them. The main one you need gone is the queen ant. I also read it's best to do it right before it rains since the water will speed the process. I have also watered the hill, after applying the grits, with a watering can. Again this does work for me but I never used it on any other kind other than the black ants in my yard. We are fortunate not to have fire ants.
Some people will say it didn't work for them or it's not true that the ants can eat the grits. I only that I do use the instant kind of grits and sprinkle them generously before rain, and they are gone in 1-2 days. I also buy the store brand for even more savings. I like it since I'm not using chemicals in my yard, and safe to use around kids and pets.