Jim Wetterer has a paper out in Myrmecological News detailing the global spread of the ghost ant Tapinoma melanocephalum. This diminutive dolichoderine is quite possibly the most widely distributed ant in the world, a hitchhiker on human globalization, thriving in the wake of human-wrought ecological destruction. Their cosmopolitan dominance reflects our own.
Oddly enough, we still don’t even know where they originally lived.
Ghost Ants - photo by Picasa user Aimeric
citation: Wetterer, J. K. 2008. Worldwide spread of the ghost ant Tapinoma melanocephalum (Hymenoptera: Formicidae). Myrmecological News 12, 23-33.
Myrmecos Blog 
“Oddly enough, we still don’t even know where they originally lived.”
That’s a common theme with synanthropic species, unfortunately. Just look at all those misnamed cockroaches: Blatta orientalis (From the Orient? Maybe.), Blattella germanica (From Germany? Almost definitely not), Periplaneta americana (Um, yeah – probably not American originally). Then there are the cosmopolitan parasitoid Hymenoptera I work on: Evania appendigaster (L.) (Evaniidae), Prosevania fuscipes (Illiger, 1807) (Evaniidae), Trichosteresis glabra (Boheman, 1832) (Megaspilidae), and Aphanogmus fumipennis Thomson, 1858 (Ceraphronidae). Where did any of these originate? Who knows. I’m not even 100% sure how we would figure that out! Maybe some sophisticated techniques borrowed from our population genetics colleagues…I have some ideas anyway of things to try.