Behold the lowly ant!
Many of us have explored an ant colony during an early part of our biology curriculum. At school or at home, we set up an ant farm in some dirt between two glass panes in a wooden frame. If we successfully relocated a breeding queen ant and her entourage, we might be lucky to observe a couple hundred specimens burrowing away behind the glass.
Fast forward to 2002 and visit southern Europe (Italy, France, Spain or Portugal) to be awed by the world's largest ant colony, extending over a territory of 5760 kilometers and comprised of several billion ants. This is the largest ever known community of cooperating living beings.
Ants are a successful insect species and can be found practically all over the world. But up until now, the colonies in individual nests formed by their respective queens were observed to be independent, and often mutually hostile. It is novel and perhaps frightening to take note of the new exception to this rule: Argentinian ants (Linepithema humile), accidentally imported into Europe some 80 years ago, were apparently very successful in colonizing their new habitat. Nest density was high, so evolution favored cooperative rather than competitive behavior. It's amazing to see Darwin at work in such a short time span, and the result is evident: Cooperating nests of Argentinian ants have wiped out more than 90 percent of all other ant species in their territory.
Genetically, the ants making up the gigacolony in southern Europe are similar enough that any colony member can recognize any other colony member as a relative in spite of having been bred from different queens. Italian ants dropped in a nest in Spain will help with the establishment of the colony, whereas insurgents from other ant groups are immediately attacked and killed. In fact, a similar but distinct and smaller colony of Argentinian ants exists in the Catalan region in the north of Spain. Ants from the gigacolony and those from the Catalan show the normal ant behavior of fighting to the death when they meet.
Scientists believe that the overwhelming success of this ant colony may be its undoing in the long term, as the worker ants raising a queen's offspring are becoming more and more distantly related to their charges. Eventually there may be enough genetic diversity to schism the colony into disparate groups.