Apparently, they're the most successful species of ant because of their unique nature to not compete or attack other Argentine ant colonies. Whereas other groups of ants would attack any surrounding nest, regardless of species, the Argentine ants would work together and "mingle" with other separated nests.

I read that in Wiki after reading an article about ants in the news, but the most interesting bit of info I learned was this:

Researchers from the University of California, Irvine, have developed a way to use the scent of Argentine ants against them. The exoskeletons of the ants are covered with a hydrocarbon-laced secretion. They made a compound that is different, but similar, to the one that coats the ants. If the chemical is applied to an ant, the other members of the colony will kill it.

So, essentially, you could spray an ant, and its colony would recognize its different scent as that of an enemy's and kill it. Wicked.