I like to avoid toxins as much as possible, and use effective, yet non-toxic means for pest control when possible.
Mixing borax or diatomaceous earth with some powdered sugar (there's also supposed to be a binder, but I don't remember what it is, you might be able to find it on the internet) will kill them. The sugar attracts them, they grab the ball of stuff to take back to the hive. The queen chows down, and the hive is done for. I'd do a search on "kill ants natural" or "ants diatomaceous" or, probably even better, "natural pest control ants" to find a site with some other natural options.
Sprinkling diatomaceous earth (the fossillized remains of some microscopic creatures) in the corners or where you think they are coming in can also work. From an insect point of view, it is very sharp. It works with any hard-shelled insects like ants, roaches, etc. by cutting into the shell and exposing their soft body parts to air, thus drying them out. Totally non-toxic to humans and pets, though you don't want to get it in your eyes. It's also used in human and pet supplements. (When building a new house, it's a good idea to sprinkle it in the walls, that way you have long-term pest control that is invisible and won't be in your living space).
I've sprinkled DE on ant hills outside (too close to the front door, and they crawled up my leg when I was tending my garden), and it caused an immediate exodus of ants from the area. They never came back! And I know it's not harmfull to me or my cats.