Get some
Acephate from Gillis Feed Store (or other feed store). Put it on the beds late in the afternoon and in about a day they are dead. Some move a few feet away so I treat them too and that usually does it. Stuff stinks to high heaven! Put 2 cans in my trunk and had to roll windows down about a mile or so later!
http://www.pestmall.com/fire-ant-killer-acephate.html