We had little black ants come into the kitchen the spring after we bought our house and the local farm supply store recommended a product called Terro. Its a syrup like liquid that you put on small squares of thin cardboard and place where they enter. They swarm over it sucking up the poison and take it back to the nest. Really worked for us. Have had one attack of ants in 11 years since and used the same treatment. Gone in a few days.