Taxonomy and distribution of the argentine ant (Linepithema humile) (Hymenoptera: Formicidae)

*[Linepithema humile (Mayr) 1868 is confirmed as the valid name for the Argentine ant. Morphological variation & species boundaries of L. humile are examined, with emphasis on populations from the ant's native range in southern South America. Diagnoses & illustrations are provided for male, queen, & worker castes. Collection records of L. humile in South America support the idea of a native distribution closely associated with major waterways in lowland areas of the Paraná River drainage, with recent introductions into parts of Argentina, Brazil, Chile, Colombia, Ecuador, & Peru.]