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Lasius alienus is a dull brown species with lighter brown appendages, dense pubescence, and a truncated propodeum. Under the current taxonomic concept (Seifert, 1992; Wilson, 1955), L. alienus has one of the most widespread native ranges of any ant species, spanning the Holarctic from the west to east coast of North America through Western Europe and Central Asia east to Japan. Whether these widely separated populations truly represent a single species or are actually a complex of cryptic species is a question of some debate (Seifert, 1992;2009). The bi-continental distribution, perhaps together with the unfortunate specific epithet, has caused led some to consider L. alienus an alien species in North America (Maerz et al., 2009; McGlynn, 1999a). While the North American population may well prove to be a species distinct from the Eurasian populations, the preferred habitats, broad distribution and general biology suggest that its occurrence on the continent preceded the arrival of humans. The ants are monogynous, eat both dead and live insects, gather nectar from the floral and extrafloral nectaries of plants, tend honeydew-excreting insects, and foster and transport certain subterranean plant lice from the roots of one plant to another. These latter habits cause L. alienus to sometimes be considered an agricultural pest (Smith, 1965). The species is also considered a house pest in some areas, as it is tends agricultural pests and is prone to enter dwellings in search of food and shelter (Smith, 1965; Thompson, 1990). The name ‘Cornfield Ant’ is sometimes applied to Lasius species, including L. alienus, but its use is perhaps better confined to L. neoniger which was discovered to have a mutualistic relationship with corn root aphids.