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Species: Lasius (Lasius) alienus   (Foerster, 1850) 

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See Also:

Lasius alienus barbarus, Lasius alienus pannonica, Lasius alienus pontica

Taxonomic History (provided by Barry Bolton, 2014)

Formica aliena Foerster, 1850a: 36 (w.m.) GERMANY. Palearctic. AntCat AntWiki

Taxonomic history

Senior synonym of Lasius americanus, Lasius pannonica and material of the unavailable names Lasius alienoamericanus, Lasius flavidus, Lasius turkmenus referred here: Wilson, 1955a PDF: 77.


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. 


Current range (Wilson, 1955): In Eurasia it is found from the British Isles and southern Fennoscandia south to Morocco-Tunisia, east through Lebanon and Iraq to Kashmir and southern China, and north into European Russia, central Asia, China, and Japan. Does not occur in the Balearics, Canaries, and Azores, or in Formosa. In North America it is found from southern British Columbia to Nova Scotia and south to the mountains of Durango, Mexico, in the west, and to northern Florida in the east.

Throughout SLO except S & NE


It is well recognized that the ecology of the North American and Eurasian populations of L. alienus differ considerably. In the Central Europe L. alienus is found in xerothermous, non-urban habitats of differing horizontal and vertical plant structure such as bare rocky areas, dense grasslands, orchards, sunny forest margins or warm woodlands with sparse canopy cover (Seifert, 1992). In North America alienus prefers well shaded woodland, where it nests in rotting logs and stumps and under stones (Wilson, 1955). Wilson argued that the ecological differences between the two populations were caused by competition with the congeneric species, but Seifert believes the North American population is a distinct species (pers. comm.). 


Diagnosis among workers of introduced and commonly intercepted ants in the United States. Worker caste monomorphic. Antenna 12-segmented. Antennal club indistinct. Antennal scape length less than 1.5x head length. Eyes medium-sized (greater than 5 facets). Three distinct ocelli present. Mandibles with 8 (rarely 9) teeth including 3 basal teeth. Promesonotum separated from propodeum by metanotal groove, but not by a deep and broad concavity. Propodeum and petiolar node both lack a pair of short teeth. Propodeum lacking posteriorly projecting protrusion. Propodeal declivity at least twice length of propodeal dorsum. Metapleuron with a distinct gland orifice. Waist 1-segmented. Petiole upright and not appearing flattened. Gaster armed with acidopore. Distinct constriction not visible between abdominal segments 3+4. Erect hairs present on mesosoma, but not long thick and produced in pairs. Head length = 0.75–0.97 mm. Head width = 0.68–0.92 mm. Scape length = 0.72–0.89 mm.

Lasius alienus specimens from Europe, which are commonly intercepted at US ports of entry, cannot be distinguished from North American specimens using any current methods. The species can be separated from introduced and other commonly intercepted formicine genera by the combination of the following characters: (1) antenna 12-segmented; (2) monomorphic worker caste; (3) three distinct ocelli; (4) metapleural gland present; and (5) propodeal declivity at least twice length of propodeal dorsum. Separating L. alienus from the invasive L. neglectus (which is at risk of establishing in North America) is difficult. The mandibles of L. alienus have eight (or rarely nine) teeth, three of which are basal (versus seven or rarely eight teeth, two of which are basal in L. neglectus).  Lasius alienus is also relatively larger (HW = 0.68–0.92 mm, versus 0.64–0.81 mm in L. neglectus), with generally longer antennal scapes (SL = 0.72–0.89 mm, versus 0.68–80 mm in L. neglectus). Lastly, L. alienus is monogynous while L. neglectus is polygynous. Additional morphometric characters used to separate the two species are available in Seifert (1992)and partially summarized in Espadaler & Bernal (2004), but beware that these characters are averaged across workers of entire colonies.


One wonders if the old name americanus might be valid for this American population?

Taxon Page Author History

On 2012-07-25 17:14:13 Eli Sarnat modified Identification
On 2012-07-20 18:31:19 Eli Sarnat modified Identification
On 2012-07-20 18:29:59 Eli Sarnat modified Biology
On 2012-07-20 18:29:01 Eli Sarnat modified Distribution
On 2012-07-20 18:27:41 Eli Sarnat modified Overview
On 2011-03-31 23:46:13 Eli Sarnat modified Distribution
On 2011-03-31 23:46:13 Eli Sarnat modified Biology

Taxonomic Treatment (provided by Plazi)

Forel, A., 1890:
Laverdure (sur les chênes-liège ); Bône .

Ward, P. S., 2005:

Andre, E., 1887:
Ouvriere: Antennes de 9 articles. Tout le corps lisse et tres luisant. D'un brun-marron fonce, presque noir; mandibules et partie anterieure de la tete plus rougeatres; antennes, articulations des pattes et tarses d'un jaune sale. Pubescence nulle; pilosite tres eparse; funicule avec une pubescence un peu relevee et assez abondante. Pronotum et mesonotum formant ensemble (vus en dessus) un hemisphere un peu aplati; mesonotum separe du metanotum par un profond etranglement; face basale du metanotum horizontale, au moins aussi longue que sa face declive. Ecaille cuneiforme, un peu inclinee en avant, tres epaisse a la base, amincie et plus ou moins echancree au sommet. - Long., 1 2 / 3 - 2 mill.
Parait etre voisine de la M. Kraatzi Roger , qui ne m'est connue que par la description de son auteur, mais s'en eloigne par sa couleur tout autre et par la conformation de son petiole.

Forel, A., 1894:
Himalaya, 9,000 ' de hauteur (M. Smythies). [[ queen ]] L. 2, 7 a 3, 2 mill. Pas de sillon frontal distinct. Brunatre, avec le thorax les antennes et les pattes plus clairs. Scapes et pattes sans poils dresses. Comme les petits exemplaires clairs d'Europe.

Specimen Habitat Summary

Found most commonly in these habitats: 0 times found in Unknown, 0 times found in Rocks (rocky-calcareous grasslands), 0 times found in Pinyon-cedar woodland, 0 times found in heathlands, 1 times found in Meadow, 0 times found in Mixed hardwood forest, 0 times found in Short grass prairie, 0 times found in shortgrass prairie, 0 times found in pinyon-cedar-oak woodland, 0 times found in Mixed canyon forest, ...

Collected most commonly using these methods or in the following microhabitats: 2 times Under rock, 2 times pitfall trap, 47 times search, 0 times Manual catch, 0 times log stage 4, 0 times under log, 3 times winkler, 2 times log stage 3, 6 times Bay Area Ant Survey (BAAS), 0 times log stage 5, 1 times leaf litter on river shore, ...

Elevations: collected from 5 - 3170 meters, 1329 meters average

Type specimens: syntype of Formica aliena: casent0915591; syntype of Lasius niger americanus: casent0905677

(-1 examples)

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