I caught an interesting article from BBC Earth News last night that involves a study of 'super-colonies' among Linepithema humile (Argentine ants). The general idea behind the report is that transplanted ants from the Paraná River basin have set up massive-sized colonies stretching along the coasts of the Mediterranean (6,000km), southern California (900km), and western Japan. These ants all share a common genetic make-up, which means that groups from neighboring sites do not attack one another as they would within other ant populations. In particular, the chemical make-up of hydrocarbons on the ants' cuticles seems to hold the key in recognizing friend from foe.

According to the BBC piece, representatives from all of the super-colonies "rubbed antennae with one another and never became aggressive or tried to avoid one another". Meanwhile, those from 'smaller' colonies (in Catalonia, Spain and Kobe, Japan) were very aggressive toward their colonial brethren -- the ants taken from the super-colonies of the Mediterranean and western Japan. And what does "very aggressive" mean? Well, the San Diego Union-Tribune has a piece on Argentine ants that mentions research conducted by David Holway, Andrew V. Suarez, et al. and includes the following:

At territorial boundaries where ants of different colonies confront each other, full-fledged battles are frequent, murderous and epic on a miniature scale.

During one six-month study, for example, Thomas [Melissa Thomas, a University of California-San Diego postdoctoral fellow involved with the study] estimated that border skirmishes around one of the smaller colonies at Lake Hodges resulted in the deaths of at least 15 million workers.