The Argentine ant, Linepithema humile, is among the world’s most notorious, successful and well-studied invasive ant species. Linepithema humile is a nondescript, soft-bodied, small (2.2–2.6 mm), dull light to dark brown ant with large inset eyes. The species is native to the Paraná River drainage in South America, which stretches across northern Argentina, Uruguay, Paraguay, and southern Brazil (Wild, 2004). Linepithema humile thrives in Mediterranean climates, and over the past century it has spread to across the globe by human-mediated transport to Chile, western and southern North America, Hawaii, New Zealand, Easter Island, Australia, Japan, Africa, and southern Europe (Suarez et al., 2001; Wetterer et al., 2009). Argentine ants are significant pests, and are documented to cause substantial harm to native arthropod communities (Cole et al., 1992; Rowles & O'Dowd, 2009a), vertebrate communities (Suarez & Case, 2002; Suarez et al., 2005), plant communities (Christian, 2001; Ives et al., 2011; Lach, 2005; Rowles & O'Dowd, 2009b). Argentine ants are also significant agricultural pests (Vega & Rust, 2001)and urban/residential pests (Klotz et al., 2008a; Klotz et al., 2008b).
Argentine ants are significant ecological, agricultural, and urban/residential pests.
Diagnosis of worker among Antkey species. Antenna 12-segmented. Antennal scape length less than 1.5x head length. Eyes medium to large (greater than 6 facets); do not break outline of head; placed distinctly below midline of face. Antennal sockets and posterior clypeal margin separated by a distance less than the minimum width of antennal scape. Anterior clypeal margin variously produced, but never with one median and two lateral rounded projections. Mandible lacking distinct basal angle. Profile of mesosomal dorsum with two distinct convexities. Dorsum of mesosoma lacking a deep and broad concavity; lacking erect hairs. Promesonotum separated from propodeum by metanotal groove. Propodeum with dorsal surface not distinctly shorter than posterior face; angular, with flat to weakly convex dorsal and posterior faces. Propodeum and petiolar node both lacking a pair of short teeth. Mesopleura and metapleural bulla covered with dense pubescence. Propodeal spiracle bordering posterior margin of propodeal profile. Waist 1-segmented. Petiole upright and not appearing flattened. Gaster armed with ventral slit. Erect hairs lacking from cephalic dorsum (above eye level), pronotum, and gastral tergites 1 and 2. Dull, not shining, and color uniformly light to dark brown. Measurements: head length (HL) 0.56–0.93 mm, head width (HW) 0.53–0.71 mm.
Among the species treated here, Linepithema humile is most easily confused with the Argentine Ant, L. iniquum. It can be separated from that species by the following characters: (1) the mesopleura and metapleural bulla are covered in pubescence and have a dull (versus glabrous) surface; (2) erect hairs are lacking (versus present) on cephalic dorsum (above eye level), gastral tergites 1 and 2, and often present on pronotum; (3) the profile of mesosomal dorsum has two (versus three) distinct convexities; (4) the propodeum is angular (versus globular) and is flat or weakly convex with dorsal and posterior faces (versus strongly and uniformly convex); and (5) the propodeal spiracle is bordering (versus distinctly anterior to) the posterior margin of propodeal profile.
Linepithema iniquum, Iridomyrmex anceps
Native range. Paraná River drainage in South America.
Introduced range. Chile, western and southern North America, Hawaii, New Zealand, Easter Island, Australia, Japan, Africa, and southern Europe.