If you can see where they are getting into the house, try sealing up the openings. I did find a good recipe on the internet for a borax based ant killer. I think one of these might be it? http://www.stacymakescents.com/homemade-ant-baithttp://boraxantkiller.com/step-by-step-instructions/
We've always had a ton of ants in the yard, but this year they keep trying to get in the house! We seal up one spot, they find another. Can anyone recommend a good exterminator? Preferably one who isn't trying to push a monthly service contract.