We've had a problem with ants for years - I think there's a big nest under the house! It's an old cottage with no proper foundation, so they seem to be able to get right under and emerge in a few places in the middle, near the chimney. Not much of an issue most of the time, except when they decide to get wings and take flight when we get warm, humid weather in summer.
I've tried various treatments- powders, sprays etc. Nippon syrup which has a poison they bring back to nest, had worked years ago, but they weren't attracted to it recently. Then last year I found the ants swarming over the lid of a honey jar. I mixed the Nippon with some honey and left it in their path - the lid it was on was soon swarming with ants traveling back and forth and the next day there were none!