Interesting post Wiz. We have had two known incursions of fire ants in New Zealand and both were brought under control. One was at an airport the other a seaport, ants probably came via imported goods . There are several other species of ants that have become established here too which are probably in the US as well, for example the Argentine Ant
Picture of Fire Ant mounds
source: Dept of Entymology . Texas A&M Univ.