“Borax ant bait
Borax is the most common ingredient in house ant control products, and get this: it’s absolutely 100% natural. The best way (in my opinion) to use Borax is to mix 1 cup of warm water with 1/2 cup of sugar, and 2 tablespoons of Borax. Then soak the Borax mixture up with cotton balls and place those cotton balls near any trails the ants have established in your home.”
I’m not sure where I emailed this to myself from (source) but apparently it works.
Of course I must remind you that any poisons (natural or not) must be used with due care and caution… gloves, etc, and away from children…