Last summer my mom came up and sprayed a bunch of chemicals around our house because I had told her we had ants (she was very well meaning, but I wish she had asked first!) After she sprayed, instead of having an ant here and there, we had HUNDREDS, and they were everywhere...surprisingly not in the food...luckily. We waited for the poisons to work, but these suckers are tough. Ant traps don't touch these bad boys either. So I did some research online and found that Borax is supposed to work.
I guess they think that the Borax is food and bring it back to their queen who ends up dying, and then then the other ants either leave or die as well. Luckily we use Borax for our homemade laundry soap, so it is always available. I put a thin layer of the stuff at the back of our counters, and within a few days we noticed that the ants were gone. Or maybe they were hiding, since they are back this year. Today I will be putting Borax around the counters and hoping that they disappear again...especially since we are to have company Friday afternoon. Nothing says "Welcome!" like big fat carpenter ants crawling on your walls!