The Argentine ant, Linepithema humile (formerly Iridomyrmex humilis), is an ant native to northern Argentina, Uruguay, Paraguay, Bolivia and southern Brazil. It is an invasive species that has been established in many Mediterranean climate areas, inadvertently introduced by humans to many places, including South Africa, New Zealand, Japan, Easter Island, Australia, Europe, Hawaii, and the continental United States
The worker ants are 1.6–2.8 millimetres (0.06–0.11 in) long and can easily squeeze through cracks and holes as small as 1 millimetre (0.04 in) in size. Queens are 4.2–6.4 millimetres (0.17–0.25 in) long, much smaller than other species of ants. These ants will set up quarters 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.[
The ants are ranked among the world’s 100 worst animal invaders. In its introduced range, the Argentine ant often displaces most or all native ants. This can, in turn, imperil other species in the ecosystem, such as native plants that depend on native ants for seed dispersal, or lizards that depend on native ants for food. For example, the recent severe decline in coastal horned lizards in southern California is closely tied to Argentine ants displacing native ant species on which the lizards feed.
Argentine ants sometimes tend aphid colonies,[ and their protection of this plant pest from predators and parasitoids can cause problems in agricultural areas. In return for this protection, the ants benefit by feeding off an excretion known as honeydew. Thus, when Argentine ants invade an agricultural area, the population densities of these plant parasites increase and so does the damage they cause to crops. There is also evidence that the presence of Argentine ant may decrease the number of pollinators that visit natural flowering plants via predation on the larvae of the pollinator