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Linepithema humile (Family Formicidae)

Argentine Ant

Distribution:

Although the Argentine ant is native to Central and South America, it has been transported by human activity to North America, Europe, the Canary Islands, the Azores, southern Africa and Hawaii. Within Australia, it occurs in the Sydney region (Lane Cove, Birchgrove, Strathfield, Mascot) and Stanwell Park, and the Australian Capital Territory. It is also widely distributed in Victoria; present in Adelaide and the adjacent hills; in Hobart and Launceston, Tasmania, and in several Western Australian urban centres between Geraldton and Esperance (Albany, Bunbury, Collie, Nannup, Perth, and isolated occurrences in bushland in the Darling Range and in the deep south-west of the state). (NSW, ACT, VIC, SA, TAS, WA)

Features:

The Argentine ant is a small, light brown to dark brown ant (2.2 – 2.6 mm). The eyes are placed low down on the head capsule and close to the insertions of the antennae. Each mandible has 5 – 8 large teeth and 5 – 13 smaller denticles, and the anterior margin of the clypeus is slightly concave.

Ecology/Way of Life:

Unlike many native Australian ants, Argentine ants have many queens, a social system termed polygynous (from Greek poly = many; gyne = female). These ants are successful for several reasons. Firstly, this species is well-suited to nesting in patchy and unstable sites which are naturally poor in ant species. Such sites are common in human environments. Argentine ants can establish nests in places like lawns, gardens, the bases of potted plants, in wall cavities and in rubbish. In addition, because they have many queens, Argentine ants can build up huge numbers relatively quickly in such sites. They have also lost the natural territoriality found in many ant species, so that workers from more than one nest will combine in a particular task, for example, when overpowering other species of ants. Scientists have suggested that this readiness to accept other colonies of their own species is the result of loss of genetic diversity. Lastly, unlike most other ants, Argentine ants do not found new colonies after flights by queens that have mated. Instead, queens in established nests begin new colonies after moving out on foot, attended by a group of workers. This process is called budding.

The wide range of foods eaten by Argentine ants also contributes to their success. They feed on a wide variety of naturally occurring foods, including insects, seeds, nectar and honeydew, and tend scale insects and others that produce such foods (see Fig. 1). However, they also eat processed foods found in human habitations, and in particular, they prefer sweet foods with a high sugar content.

Interaction with Humans/Threats:

Where they occur, Argentine ants are a major domestic nuisance. However, they are also an important threat to native ecosystems because of their ability to out-compete native ant species or destroy them directly, and their tendency to eradicate other invertebrates and even small ground-living vertebrates. Argentine ants can restrict the setting of seeds in some plants (for example, they have severely damaged the Protea industry in South Africa), and they can affect egg production in open-range chicken farms.

Other Comments:

Described by G.L. Mayr in 1866, the genus name Linepithema is based on the Greek: linon = linen; and epithema = a coat or covering; Mayr described the species humile in 1868, from the Greek: humilis = earthy or low. This species was initially thought to belong in the genus Hypoclinea, and then in Iridomyrmex. Steve Shattuck subsequently combined Linepithema with humile in 1992.

Further Reading:

Holldobler, B. & Wilson, E. O. (1990). The Ants. Cambridge, Mass.: Harvard Univ. Press. 732 pp.

Shattuck, S. O. (1999). Australian Ants/Their Biology and Identification. Collingwood, Vic.: CSIRO Publishing. 226 pp.

Lanthrop, K. & Valdellon, B. (1999). Argentine ants. http://www.insecta-inspecta.com/ants/argentine/index.html

Robertson, H.G. (2004). Linepithema humile (Argentine ant). http://www.museums.org.za/bio/ants/dolichoderinae/linepithema_humile/index.htm

Krushelnycky, P. & Suarez, A. (2005). Global Invasive Species Database Linepithema humile. http://www.issg.org/database/species/ecology.asp?si=127&fr=1&sts=

Acknowledgments:

Dr M. Malipatil (Agriculture, Victoria) and Dr Murray Fletcher (NSW Agricultural Scientific Collections Unit), who kindly provided information on the occurrence of the Argentine ant in Victoria and New South Wales, respectively; text and map by Brian Heterick/ Curtin University, Perth; photograph courtesy of HG Robertson / South African Museum.

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