Boiling water works for me. We have had big problems in the past with ants but have always had success with boiling water. My granny used it too when she was alive and she was the daughter of a market gardener and a very wise woman. That would be my recommendation anyway.
Not very PC but I am inclined to think ants are rather pointless. Ooops...I am bound to have upset someone now aren't I!
Good Luck,
Rachel