The subterranean portion of a fire ant mound can cover an acre. There may well, and in large colones there likely are multiple queens. What ever you try by all means DO NOT disturb the mound. Disturbing the hill or mound will only result in the ants creating a new mound in a different location, which may trick you into believing that you have succeed in destroying the colony. The best pesticide for fire ants is the same one that works so well against chicken mites, Pyrithian. Do not spray the mound or disturb it in any fashion, instead use a bait like Amdrol. Adult fire ants are unable to eat solid food. All fire ant food is first fed to the fire ant young and the ant larva eat and digest this food then regenerate part of it in liquid form. the adult ants consume this liquid food. The ant larva die first and that leaves the worker ants without a food source so they starve.