"Perhaps the most economical and effective way to get rid of carpenter ants is by applying boric acid (also known as borax) to their nest sites and surroundings. This natural non-toxic element, mined from below the Mojave Desert in southern California, has a long history of use in exterminating brazen populations of cockroaches, palmetto bugs, waterbugs, silverfish, termites, and, you guessed it, carpenter ants."
..."This simple, inexpensive, household chemical is deadly to all insects,”...“It has been shown to attack their nervous systems, as well as being a drying agent to their bodies.”
When I was young, the neighbors who lived behind us had a borax mine out in the desert and I remember visiting it. I grew up in southern California. This article reminded me of that visit and the adventure of climbing down into the mine.
I am going to get some borax and experiment on the ants around the house. We are surrounded by red ants and large black ants too. Looks like they go under the house. They come into the kitchen and scout around, but we are being careful to sweep crumbs and keep dishes clean on counters and they aren't finding anything to get into. It will be interesting to see how the borax discourages the ants from coming into the house.