Mix together 1 teaspoon sugar and 1 teaspoon borax. Add enough water to make a paste and leave where you see ants outside. The lid from a plastic container would work well. I had ants in one of my trees and spread some of the paste across their trail. Within two days all the ants were gone. (Hopefully they took some of the paste back to the nest).
Other recommendations are to water it down and spray it on the ants.
Make sure to keep the mixture away from pets and other animals.
Note: You can find Borax in the laundry aisle.