If you see a 2 to 3 milimeter sized ant and you just so happen to live either in the western coastal states of the US, or in Europe, or in Japan, or in the South Island of New Zealand, or in the southern half of Australia, then you see a member of the largest ant colony in existence.
And all because some 19th century folk from the Parana river valley accidentally brought some argentine ants to Madeira and New Orleans...