Answer: I'd suggest starting with boiling water poured on the hill.
You can also try diatomaceous earth. Generally that's used for slugs and snails but I've heard of success with ants as well. Diatomaceous earth consists of the skeletal remains of little single-celled marine algae. It kills by lacerating the bodies of soft-bodied pests, causing dehydration. You could sprinkle it right on the hills. The best time to use this is during hot, dry weather. It doesn't hurt mammals, birds or earthworms, although it can harm some beneficial insects. Don't put it on flowers in order to protect the pollinators (bees). Also, protect yourself from irration of eyes and lungs. Do it on a quiet day-no wind! Buy agricultural diatomaceous earth, not the pool-grade variety, which lacks that power to "cut".
Soap sprays are helpful if applied directly on the pests and boric acid sprinkled along the foundation of the house and in front of the doorway can also keep the ants at bay. Hope the above suggestions help you get a handle on the pests!
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