Fire ants spread by both natural and artificial means.
This is why certain materials likely to harbor fire ants, including nursery stock, sod, and hay, must be certified as fire ant-free before they are sold outside the fire ant quarantine area.
Entire colonies can move from one location to another when they are disturbed, but they generally don't move far. Winged fire ant queens can fly quite a distance on their own. Studies have shown that distance to be limited to three miles or less, based on their energy reserves. When blown by wind currents, winged fire ants can travel much greater distances.
Find more information about fire ants in eXtension's Imported Fire Ant Resource Area.