I've fought this battle off and on for decades. I'm fingers crossed right now, was thinking about this just this morning. Haven't spotted an ant in the house for something like two years now, knock on wood.
My advice:
Don't spray poison. There's too much poison around and especially you don't want to spray it in your house. It's not necessary.
I have used baits you buy in the store. Sometimes with success, other times not. The best method I've found was in a newsgroup. It was posted by a professional who deals in this stuff all the time. Here it is out of my data:
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Select a product with boric acid. "Terro" is one such product. The application requires placing the bait on small squares of thin cardboard. Once the ants discover the food source you'll see hundreds of ants carrying the bait back to their nest and in 2-3 days they will be gone. You do not need to spray insecticides and these won't kill the queen anyway.
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Here's a good one from the thread:
He's responding to my question whether the ants could be nesting in my walls because I couldn't find where they were outside, where they were coming in...
That could be a slim possibility. I would stay outside and keep looking out there. Roll over rocks, move any items sitting flat on the ground, turn over landscaping timbers if any, pull back mulch and look under it. I have learned that if you want to get the ants out of the house DO NOT put bait on the inside. Too many times I go to a home where either the homeowner, or another PCO has been baiting on the inside, and they all seem to say the same thing, "it seems to get worse after they bait." I wonder why. AFTER
looking where I told you, if you are still having a hard time finding them, do this:
Boil about three cups of water with 1 cup of sugar, once the sugar has melted remove it from the heat, take an old sock and place a slice of apple in it and drop it in the water for about 10 minutes. place it on the outside of the house by the room where the ants are. Leave it and go back a day later, and there should be numerous ants, then you can easily trace their trail to where the nest is. Once you find that, then bait where the nest is and you should eliminate the problem. Also remember to remove the apple and the sock after the second day, because if you don't, you may attract other ants. Good Luck to you
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I have used the sock, apple and sugar water method, followed by baiting outside, several times with success. You can buy orthoboric acid cheap in quantity at a hardware store.