[header] How to kill ants [title] Sprinkle diatomaceous earth around problem areas. [step] Apply a fine layer of de anywhere you notice ants gathering in, focusing on points of entry, major food sources, and nests. [substeps] Only use food-grade de. 
Some de is used for cleaning swimming pools, but this variety usually contains pesticides and other chemicals that can be toxic to pets and small children if ingested. On the other hand, food-grade de is non-toxic.