We occasionally get ants in the house and usually have them in the yard around our house. I'd read that boric acid is used in poisons for both roaches and ants, so I decided to try to make some for my own use.
I bought a bottle of Boric Acid Powder at the Pharmacy at WalMart. We had a bottle of Karo Light Corn Syrup with Vanilla in the cupboard at home.
I mixed one and three-quarters teaspoons of boric acid powder with 4-fluid ounces of water and 4 fluid-ounces of Karo Syrup. (Any sort of syrup, or honey, will probably work.) The boric acid did not dissolve, so I heated the mix for 55 seconds in the microwave and then stirred. Not all the boric acid dissolved, so I set the timer for another 55 seconds and turned it off when the mixture began to foam. I stirred again to dissolve the remainder of the boric acid. I placed this into a pint jar labeled "Ant Poison".
In the house I put a small puddle of poison onto a one-inch square of cardboard where I saw the ants moving around in the kitchen. This seemed to take care of them within several days.
We had some left over grease from cooking, so I heated about three-ounces of grease in a small container in a pan of boiling water and added three-quarters of a teaspoon of boric acid powder. I mixed this in well, then cooled the grease in the refrigerator. I put some of the cooled grease out with the syrup poison, but by this time the ants had pretty well disappeared from the kitchen.
I've been using an old disposable dropper from the lab to put a dose or two of the syrup poison, usually on a tree leaf, onto the anthills outside around the house - a dose or so every day that I can. One hill became completely inactive in about a week, a second became inactive, then I found ants in it again. I've been trying it on several other anthills around the house.