Ants are conspicuous components of most terrestrial ecosystems. Ants are important predators, scavengers, granivores, and in the new world, herbivores. Ants also engage in an astonishing array of associations with plants and other insects, and can act as ecosystem engineers as agents of soil turnover, nutrient redistribution, and small-scale disturbance.

Over 15,000 species of ants have been described, and more than 200 have established populations outside of their native ranges. A small subset of these have become highly destructive invaders including the Argentine ant (Linepithema humile), the big-headed ant (Pheidole megacephala), the crazy ant (Anoplolepis gracilipes), the little fire ant (Wasmannia auropunctata), and the red imported fire ant (Solenopsis invicta) which are currently listed among the world’s 100 worst invasive species (Lowe 2000). Additionally, two of these species (Linepithema humile and Solenopsis invicta) are among the four most well studied invasive species generally (Pyšek et al. 2008). Although invasive ants are economically costly in both urban and agricultural areas, the most serious consequences of their introduction may be ecological. Invasive ants can greatly modify ecosystems by reducing native ant diversity, displacing other arthropods, negatively impacting vertebrate populations, and disrupting ant-plant mutualisms.

Invasive ants form a small and somewhat distinct subset of ants introduced into new environments by humans. A majority of introduced ants remain confined to human-modified habitats and some of these species are often referred to as tramp ants because of their reliance on human-mediated dispersal and close association with humans generally. Although hundreds of ant species have become established outside of their native ranges, most research has concentrated on the biology of only a few species.