Go down to Msc. Threads section below. This is a series of posting caled "getting rid of ants without chemicals"(posted 9646 days ago)I have also used the boiling water with good sucess at killing ants and yellow jackets, however I pour 3 to 4 gallons of water into each mound. Smaller amounts of boiling water will not reach the main portion of the colony.
BE CAREFUL! last year while doing this I was stung and jerked spilling boiling water on my leg. I now have a scar about 4" in diameter. Nothing hurts worst then a burn except maybe a kidney stone.
Fire ants mound are connected together so if one mound is attacked the workers from another mound may come to help defend.