The Argentine ant (Linepithema humile, formerly Iridomyrmex humilis) is an ant native to northern Argentina, Uruguay, Paraguay, Bolivia and southern Brazil. This invasive species was inadvertently introduced by humans on a global scale and has become established in many Mediterranean climate areas, including South Africa, New Zealand, Japan, Easter Island, Australia, Europe, Hawaii, and the continental United States. Argentine ants are significant pests within agricultural and urban settings, and are documented to cause substantial harm to communities of native arthropods, vertebrates, and plants within their invaded range. Description Linepithema humile is a small-bodied (2.2–2.6 mm) ant species, dull light to dark brown in color. Within the invasion zone, ant colonies are large and include many workers and multiple queens. Argentine ants are opportunistic with regard to nesting preferences. Colony nests have been found in the ground, in cracks in concrete walls, in spaces between boards and timbers, even among belongings in human dwellings. In natural areas, they generally nest shallowly in loose leaf litter or beneath small stones, due to their poor ability to dig deeper nests. However, if a deeper nesting ant species abandons their nest, Argentine ant colonies will readily take over the space. Because the native habitat for this species is within riparian floodplains, colonies are very sensitive to water infiltration within their nests; if their nests become inundated with water, workers will collect the brood and the entire colony will move to dry ground. Austrian entomologist Gustav L. Mayr identified the first specimens of Hypoclinea humilis in the vicinity of Buenos Aires, Argentina in 1866. This species was shortly transferred to the genus Iridomyrmex, and finally to Linepithema in the early 1990s. Distribution The native range of Argentine ants is limited to riparian habitats in the lowland areas of the Paraná River drainage, which stretches across northern Argentina, Uruguay, Paraguay, and southern Brazil. Within South America, this species has spread into parts of Chile, Colombia, Ecuador, and Peru. Linepithema humile thrives in Mediterranean climates, and over the past century it has spread to across the globe by human-mediated transport. The species has become established to every continent except Antarctica and includes many oceanic islands. Argentine ants are now found in locations as distant as Chile, western and southern North America, Hawaii, New Zealand, Easter Island, Australia, Japan, Africa, and southern Europe Global "mega-colony" The absence of aggression within Argentine ant colonies was first reported in 1913