I posted this on a another ant thread and it works well
About 6 years ago we were plagued with ants and I remembered how my Father dealt with them years ago. I bought some Boric Acid powder (500 grams) from the pharmacy here in Cyprus. I mix 2 teaspoons of sugar and half a teaspoon of the Boric Acid together and then using a little boiling water stir it to a smooth paste. I then put it on the ant runs in pools about an inch in diameter and they feast for a couple of days. They take the mix back to their nest and feed to the young and then........no more ants. Safe on food surfaces and works equally well in the garden.