I had an ant problem for months at my old house until my neighbor gave me a packet of this:
Chinese Ant Poison
I set this stuff in bottle caps arount ant trails and soon, millions of ants came out of their colony to partake in the feast, including rarely seen large soldiers, winged females, and even some young queens that ususally never come out of the colony. Then the carnage began. The ants turned on each other and literally tore each other to pieces. When the holocaust was over, my house was littered with ant parts. The ants never came back in the 2 more years I lived at that house.
I don't know if this weapon of mass destruction is EPA approved or if it is a contraband product of China's chemical weapons program but it is the BEST ANT KILLER EVER.