Answer: If it were in your own yard, I'd suggest starting with boiling water poured on the hill. However, there's no way you could get water hot enough to help in your situation.
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 also helpful as is boric acid. Both of these are "home remedies" as well. This should give you some ammunition. If you need the tanks...come back and visit us again at http://www.garden.org!
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