Because of unusually low levels of intraspecific aggression, the Argentine ant can establish extremely large colonies.
This contributes to its status as a nuisance pest in homes and its ability to spread rapidly. Other negative effects of this invader include facilitation of plant feeding pest insects (for example, honeydew producing insects) and disruption of native ants, pollinators, and even vertebrates.
The Argentine ant, Linepithema humile, is among the world's most successful invasive species.
This ant has become a cosmopolitan pest, particularly in the Mediterranean climates of North America, Chile, South Africa, Australia, and southern Europe.
They have been very successful in spreading over great geographical areas, in part, because different nests of the introduced Argentine ants seldom attack or compete with each other, unlike most other species of ant.
In their invading ranges, their genetic makeup is so uniform that individuals from one nest can mingle in a neighboring nest without being attacked; so, in most of their introduced ranges they form "supercolonies".
Such ants have a social organization, called unicoloniality, allowing individuals to mix freely among physically separated nests.
These introduced Argentine ants are renowned for forming large colonies, and for becoming a significant pest, attacking native animals and crops.
In Europe, one vast colony of Argentine ants is thought to stretch for 6,000 km (3,700 miles) along the Mediterranean coast, while another in the U.S., known as the "Californian large", extends over 900 km (560 miles) along the coast of California. A third huge colony exists on the west coast of Japan.
While ants are usually highly territorial, those living within each super-colony are tolerant of each other, even if they live tens or hundreds of kilometers apart. Each super-colony, however, was thought to be quite distinct; however, it now appears that billions of Argentine ants around the world all actually belong to one single global mega-colony.
During research with these ants from different geographic areas, whenever the main European and Californian super-colonies and those from the largest colony in Japan came into contact, they acted as if they were old friends when they were observed rubbing their antennae with one another and never became aggressive or tried to avoid each other.
In other words, they acted as if they all belonged to one vast colony, despite living on different continents separated by vast oceans.