The nice thing about DE (the food grade) is that it's perfectly safe for consumption by any critters, including us! It's not a poison; it kills physically rather than chemically. At the microscopic level, the grains are very, very sharp...like shards of glass. When bugs with a hard shell get...
Thank goodness we don't have fire ants here! What awful things. I would recommend using some DE...on the chickens, in their coop and dust bathing areas. Also sprinkle a little around all the entrances to the ants' nests you can find. It does need to be dry to work, so you'd need to reapply...