Very interesting subject. We do not have fire ants here where I am, but carpenter ants are horrible! I have got to find some DE for around the house, I often worry about it because of the cat pens, but it will not harm the cats at the same time ridding ants.
We use Borax in the house as a powder. They pick it up passing through it and take it back to the nest killing the whole bunch of them. Also we had a sudden decline in fleas many years ago using borax around all the cracks and work it into carpeting, or sprinkling it under the pad.
Thanks for the subject and good luck!