I had a large concentration of ants come up on the edge of the back sidewalk. Thousands, in a bi g pile about two feet long and a foot wide. I just made a bucket full of warm water with some dish-washing detergent in it and went out and poured it on the ants.......... good bye ants.
Note: A teaspoon of dish-washing detergent in a small spray bottle with water is very effective in getting rid of many insects.
Note: Rotenone rapidly biodegrades under warm conditions, so harmful residues are minimal.
See: https://en.wikipedia.org/wiki/Rotenone