Now a couple of entomologists have traced the genes of the red imported fire ant (Solenopsis invicta), and concluded that all of them -- every single one -- can be traced to fewer than 20 queen ants. They probably arrived on one ship that docked in Mobile, Ala., in the 1930s. It only took one. There's more HERE from the Agricultural Research Service of the Department of Agriculture.
Why does it matter to know where they came from? Because many farmers would dearly love some way to get rid of them. Something better than spraying them, or picking them, painfully, off one's skin.
Hat tip to Brian Hartman in our Washington bureau for finding this.