Boric Acid
According to Good Housekeeping, boric acid or borax powder can be sprinkled along ant trails and will kill any ants that eat it. Be sure to keep the mixture away from children or pets, because it is toxic.
Cleaning Products
Some cleaning products such as window cleaner can kill ants on contact without residual toxicity, according to the University of California Department of Agriculture and Natural Resources.
Peppermint Soap
Kill ants naturally by spraying them with liquid peppermint soap diluted in a squirt bottle. This solution will keep the area smelling fresh and discourage ants from returning.
Mouthwash
Antiseptic mouthwash kills ants when sprayed in their tracks. Pour full-strength antiseptic mouthwash into a spray bottle to use this method of killing ants.