Ant's nests can be reduced in size by slowly pouring boiling water down their entrances or on the area where they raise their brood (the pupae are very often put above ground in sheltered places to pick up the warmth of the sun and speed up development). Boiling water may seem cruel, but take my word for it, there's less suffering than by poisoning. Boiling water is a treatment that can be repeated as often as you like with no permanent detrimental environmental damage. Killing ants this way is not a perfect method and the ants will generally reappear, but it is effective in the short run and is not expensive nor does it leave poison in the environment.
