I live in the South Sound WA area and have used corn meal on anthills. It does seem to work, though not instantly. Several applications are necessary so I keep a container of cornmeal nearby. It is not enough to sprinkle it on top, work it into the hill. Of 5 large hills from a year ago, 4 are completely gone. One returned and I'm treating it now. Of all the small hills, all are gone. However, I do think of the 4 large hills, some relocated. I think the trick is to find them before they get too big and douse them with cornmeal as deeply as possible. One of these huge hills is completely gone and it was 4 feet tall when I moved here!
We have harvester ants here in the desert and I have been told that cream of wheat does the same. I tried it, but haven't been consistent enough to know whether it works or not. Funny, I could only find the 'variety pack' and thought that using the flavored packets might just be tempting fate. I figured I might have them forever, but somehow, all the other packets mysteriously disappeared!