Bring down the nest.
If ants continue to raid your home, you're going to have to raid theirs. If you're able to locate the nest, you can pour several gallons of boiling water into it and that'll be that. But if you don't know where they're coming from, your other alternative is to bait them.
Commercial bait product at work
Pick your poison. Mixing boric acid powder or borax with maple syrup is the most common bait (and is what a popular commercial ant poison, Terro, basically consists of). Boric acid affects ants both externally (when in powder form; similar to diatomaceous earth) and internally (when ingested). The ants bring the poison (borax or boric acid) with them to the colony and spread it around. If you get the quantity and timing just right, you can wipe out a large colony, but it might take several weeks to a few months. A bait that's too strong will kill the ants before they make it home, and a bait that's too weak will only weaken the colony temporarily, so here are some recipes that people have had success with:
*1 cup water, 2 cups sugar, 2 tablespoons boric acid.
*3 cups of water with 1 cup of sugar and 4 teaspoons of boric acid.
Remove any deterrents (from previous steps) and wait for the ants to show up.
Don't lure new ants with the bait; you could attract new colonies.
Once there's a trail, place the bait next to it (not on it, or else you'll interrupt their march home).
If you have pets and/or children around put the bait in a jam jar. Screw the lid tightly and seal with adhesive tape. Pierce two or three small holes in the lid, and smear the outside with a little bit of unpoisoned bait. If you're concerned about the jar getting knocked over and the poisoned bait spilling out, loosely pack the inside with cotton balls.
Just to cover all the bases, leave out some peanut butter bait as well (peanut butter mixed with borax or boric acid powder). Ants' cravings vary depending on the needs of the colony (sometimes they want sweets, sometimes they want something oily) so providing both will increase the likelihood that they'll take the bait.
Give them as much fresh bait as they'll take, replenishing it as needed, and let them bring it back to their nest (no squishing or killing!). Once they've had their fill, remove all bait; you don't want to attract a neighboring colony.
A solution for getting rid of ants is easy to make! All you need is rubbing alcohol (no alcohol drinks!) dish soap and water. Get a spray bottle, making sure to wash it out very well, and place about a teaspoon of rubbing alcohol, and about a teaspoon and a half of dish soap. Then fill the spray bottle with water, about an inch away from the top, and close it up tight. Shake the solution until bubbles start to appear and then you're ready to spray! The solution is okay to use around children, just wipe up the mess. And because of the alcohol in the solution, the ants will stay clear away from it. So spray the openings of where the ants appear to be coming and going. The solution kills all bugs on contact, so you can even use it on plants! But if you do, make sure to spray the plant only twice! No matter how big or small it is; it'll keep away any ants, but other bugs might not seem affected by it.
