For those who want or need organic options for ant control: This link will take you to some organic ant control methods.  I do not know the efficacy of any of them on fire ants.
This is a link to a Natural Farming video on fire ant control   
Here is one good recipe:
One part of Boric Acid to 4 parts of Equal (sugar substitute) add a few drops of water and mixing it into a paste then placing it in the pathway of the ants. There is a reference in these links to a similar mix using boric acid. What I find in using the Equal is 100% efficiency. Equal is a known neurotoxin ants don't stand a chance. 
'A Farm for the Future' - Full Film

This is a link to a 48 minute video where a woman investigates how to turn her family's farm in Devon, England into a low energy farm for the future, and finds that nature holds the key.