Subfamily DOLICHODERINAE
Tribe DOLICHODERINI
Linepithema humile (Mayr, 1868)
"Argentine ant"

Authors: Joe A. MacGown and Ryan J. Whitehouse
Uploaded 2008; last updated 8 December 2016

Introduction
Linepithema humile (Mayr) (Dolichoderinae) the Argentine ant, is a small, brown species native to Argentina and Brazil. The Argentine ant is thought to have first arrived in the United States in coffee shipments to New Orleans sometime near 1891. Since it arrival in the U.S. it has spread eastward into the Carolinas and as far south as Southern Florida and westward into Texas and California.

Linepithema humile (Mayr) (Dolichoderinae) the Argentine ant, is a small, brown species native to Argentina and Brazil. The Argentine ant is thought to have first arrived in the United States in coffee shipments to New Orleans sometime near 1891. Since it arrival in the U.S. it has spread eastward into the Carolinas and as far south as Southern Florida and westward into Texas and California.

Taxonomic History (Bolton 2016)
Hypoclinea humilis Mayr, 1868: 164 (w.) ARGENTINA. Neotropic. Forel, 1908: 395 (m.); Newell, 1908: 28 (q.); Wheeler & Wheeler, 1951: 186 (l.); Crozier, 1969: 250 (k.). Combination in Linepithema (Iridomyrmex): Mayr, 1870: 959; in Iridomyrmex: Emery, 1888: 386; in Linepithema: Shattuck, 1992: 16. Senior synonym of Linepithema arrogans, Linepithema riograndensis: Wild, 2004: 1207. See also: Gallardo, 1916: 97; Bernard, 1967: 251; Collingwood, 1979: 33; Smith, 1979: 1418; Ward, 1987: 1; Wheeler & Wheeler, 1990: 465; Shattuck, 1994: 123; Wild, 2007: 61; Solis, Fox, Rossi & Bueno, 2010: 19.

Identification
Worker: Small (TL  ≈ 2.2–2.6 mm, HL 0.70–0.76 mm, HW 0.61–0.69 mm, SL 0.73–0.75 mm, EL 0.19–0.20 mm, MeSL 1.00–1.07 mm) (n=5) (MEM specimens). Usually uniformly brown, or somewhat bicolored with mesosoma brown and head and gaster brownish black. Head oval to triangularly shaped with dense, short, appressed setae; eyes well developed and located in front of the midline of the head; mandibles triangular with two distinct apical teeth followed by multiple denticles; clypeus with 2–6 setae that are shorter than the closed mandibles; antennae 12-segmented, lacking a club. Mesosoma: promesonotum somewhat convex; distinct promesonotal suture present; propodeum rounded, lacking teethe or denticles; entire mesosoma with dense, fine, appressed pubescence, larger erect setae lacking. Waist with a single petiolar node, node wider basally and tapering to a point apically (lateral view). Gaster not projecting over the petiole; overall slightly shiny with dense, short, appressed setae; sting or acidopore not present.

Queen: Larger than workers (HL 0.91–0.99 mm, HW 0.88–0.96mm, SL 0.91–0.94 mm, EL 0.40–0.42 mm, MeSL 2.16–2.42 mm) (n=5) (MEM specimens). Uniform dark reddish-brown to dark brown to slightly bicolored with head and mesosoma reddish brown and gaster brownish black. Head about as wide as long, squarish; with dense, appressed pubescence that does not completely obscure the shiny integument; longer, erect setae lacking; eyes large, about 1/3 or more the length of the head, located on bottom half of head; three ocelli present; mandibles triangular and multidentate; clypeus with 2–6 setae that are shorter than the closed mandibles; antennae 12-segmented, lacking a club. Mesosoma elongate, dorsum broadly convex with mesocutellum rounded; propodeum unarmed; entire mesosoma lacking sculpture, shiny beneah dense, short, appressed setae; long erect setae lacking. Wings transluscent yellowish brown fading to clear at bottow and apical edges; forewing with brown pterostigma and with closed costal, basal, subbasal, anal, discal, and two submarginal cells; hindwing closed basal and subbasal cells. Waist with single petiolar node, node wider basally and tapering to a point apically (lateral view). Gaster does not overhang the petiole; integument shiny beneath dense, short, appressed setae; longer erect setae lacking except for a few on apical sternites; sting or acidopore lacking.

Male: Small, slightly larger than workers (HL 0.64–0.67 mm, HW 0.66–0.69 mm, SL 0.18–0.19 mm, EL 0.34–0.38 mm, MeSL 1.59–1.76 mm) (n=5) (MEM specimens). Brown to brownish black to bicolored with head and gaster darker than the rest of the body, sometimes almost black. Head rounded posteriorly in frontal view, narrowed in lateral view; dense, appressed, short pubescence present; eyes large, about half the length of the head, located on the lower half of the head; three large ocelli present, slightly raised; mandibles small, poorly developed; when closed, the mandibles form a smooth arc; antennae 13-segmented; scape short, subequal in length with third antenomere; last 8 antenomeres shorter. Mesosoma: mesoscutum enlarged, rounded, overhanging and bulging over pronotum; scutellar sulcus deep; mesoscutellum raised above propodeum; propodeum rectangular, declivity rounded, concave, upper part overhanging petiole, lacking spines or adornment; entire mesosoma shiny, lacking sculpture, with dense, appressed, short pubescence; longer erect setae absent. Wings transluscent yellowish brown fading to clear at bottow and apical edges; forewing with brown pterostigma and with closed costal, basal, subbasal, anal, discal, and two submarginal cells; hindwing with closed basal and subbasal cells. Waist with a single small, smooth, rounded, petiolar node. Gaster sometimes overhanging petiole, shiny, lacking sculpture, with dense, appressed, short pubescence; longer erect setae absent except for a few on sternites; genitalia with small parameres.

Diagnosis
Workers of Linepithema humile can be separated other ant species in the area by their brown color, fine pubescence that dulls the integument, lack of standing erect setae, 12-segmented antennae lacking a club, single erect petiolar node, and the lack of a sting or acidopore at the apex of the gaster. Linepithema humile can be separated from the similar genus Forelius by the longer, triangular shaped mandibles and short clypeal setae that do not extend past the mandibles when they are closed. Forelius species have mandibles that are not triangular when closed with long clypeal setae that extend past the mandibles when closed. Linepithema humile is very similar to Tapinoma sessile (the odorous house ant), but differs by having an erect petiolar node rather than a  flattened node as in Tapinoma species.

Biology and Economic Importance
The Argentine ant has established itself as a major pest in the US and elsewher because of its ability to thrive numerous diverse habitats, its production of uncountable numbers of workers due to the many reproductive queens in a colony, an omnivorous diet, which enables these ants to thrive on a great variety of foods, the ability to coexist amiably with other colonies of the same species, and because they exterminate competing species of ants in their area. They nest in soil, both exposed and under cover, rotten wood, standing dead trees, refuse piles, bird nests, bee hives, and many other places. The number of individuals of this species present in an area where they are established is mind boggling with large files of workers running up and down trees, on fences, on the ground, and on other  surfaces. Though there are winged males and females, nuptial flights have not been observed (Smith 1965). Argentine ants were considered to be one of the most persistent and troublesome of the house infesting ants by Marion Smith (1965).

Due to its ability to  nest in a wide range of habitats and to utilized numerous food sources, L. humile can be a a serious household pest. Once infesting a house, these ants are extremely difficult to control or eradicate (Smith 1965). Workers of this species do not have a sting, but have been known to bite when provoked, which helps to increase their pest status (Smith 1965). Ecologically, Argentine ants may outcompete other ant species and other invertabrates in their area. They are known to be especially competitive with Solenopsis species, competing for space and food (Smith 1965).

Distribution
Native Range: Paraná River Drainage, South America (Wild 2004).

Australian: Australia, Hawaii, New Zealand, Norfolk Island, Vanuatu (AntWiki.org).
Ethiopian: Cameroon, Lesotho, Namibia, Saint Helena, South Africa, United Arab Emirates (AntWeb.org and AntWiki.org).
Nearctic: United States (AntWiki.org and MEM).
Neotropical: Argentina, Bermuda, Brazil, Chile, Colombia, Ecuador, French Guiana, Mexico, Paraguay, Peru, Uruguay (AntWeb.org and AntWiki.org).
Palearctic: Austria, Balearic Islands, Belgium, Bulgaria, Canary Islands, Channel Islands, France, Germany, Gibraltar, Greece, Iberian Peninsula, Iran, Italy, Japan, Macaronesia, Malta, Monaco, Montenegro, Morocco, Netherlands, North Korea, Poland, Portugal, Spain, United Kingdom of Great Britain and Ireland (AntWiki.org).

U.S. Distribution: AL, AR, AZ, CA, FL, GA, HI, LA, MS, NC, NM, OH, SC, TN, TX, UT (AntWeb.org and MEM).
Southeastern U.S. Distribution: AL, AR, FL, GA, LA, MS, NC, SC, TN (Antweb.org and MEM).

Acknowledgments
Funding for the ant work being done by the MEM in Alabama and Mississippi is from several sources including the National Institute of Food and Agriculture, United States Department of Agriculture, under Project No. MIS-012040, the Mississippi Agricultural and Forestry Experiment Station at Mississippi State University, with support from State Project MIS-311080, NSF Grants BSR-9024810 and DFB-9200856, the Tombigbee National Forest (U.S. Forest Service), the Noxubee Wildlife Refuge, Mississippi Natural Heritage Program Research Grant, USDA Forest Service Agreement No. 08-99-07-CCS-010, the William H. Cross Expedition Fund, and primarily by the USDA-ARS Areawide Management of Imported Fire Ant Project (2001-2014) and USDA-ARS Areawide Management Invasive Ants Project. Additionally, special cooperation has been provided by State Parks, National Forests, National Wildlife Refuges, the Natchez Trace Parkway, and from various private landowners in both Alabama and Mississippi.

Literature Cited
Bernard, F. 1967 ("1968"). Faune de l'Europe et du Bassin Méditerranéen. 3. Les fourmis (Hymenoptera Formicidae) d'Europe occidentale et septentrionale. Paris: Masson, 411 pp.

Bolton, B. 2016. An online catalog of the ants of the world. Online at: http://antcat.org. Accessed 1 October 2016.
Collingwood, C. A. 1979. The Formicidae (Hymenoptera) of Fennoscandia and Denmark. Fauna Entomologica Scandinavica 8:1-174.

Crozier, R. H. 1969 ("1968"). Cytotaxonomic studies on some Australian dolichoderine ants (Hymenoptera: Formicidae). Caryologia 21:241-259.

Emery, C. 1888. Über den sogenannten Kaumagen einiger Ameisen. Zeitschrift für Wissenschaftliche Zoologie 46:378-412.

Forel, A. 1908. Ameisen aus Sao Paulo (Brasilien), Paraguay etc. gesammelt von Prof. Herm. v. Ihering, Dr. Lutz, Dr. Fiebrig, etc. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien 58:340-418.

Gallardo, A. 1916. Las hormigas de la República Argentina. Subfamilia Dolicoderinas. Anales del Museo Nacional de Historia Natural de Buenos Aires 28:1-130.

Mayr, G. 1868. Formicidae novae Americanae collectae a Prof. P. de Strobel. Annuario della Società dei Naturalisti e Matematici, Modena 3:161-178.

Mayr, G. 1870. Neue Formiciden. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien 20:939-996.

Shattuck, S. O. 1992. Review of the dolichoderine ant genus Iridomyrmex Mayr with descriptions of three new genera (Hymenoptera: Formicidae). Journal of the Australian Entomological Society 31:13-18.

Shattuck, S. O. 1994. Taxonomic catalog of the ant subfamilies Aneuretinae and Dolichoderinae (Hymenoptera: Formicidae). University of California Publications in Entomology 112:i-xix, 1-241.

Smith, D. R. 1979. Superfamily Formicoidea. Pp. 1323-1467 in: Krombein, K. V.; Hurd, P. D.; Smith, D. R.; Burks, B. D. (eds.) 1979. Catalog of Hymenoptera in America north of Mexico. Volume 2. Apocrita (Aculeata). Washington, D.C.: Smithsonian Institution Press, pp. i-xvi, 1199-2209.

Smith, M. R. 1965. House-infesting ants of the Eastern United States, their recognition, biology, and economic importance. United States Department of Agriculture, Technical Bulletin No. 1326: i–105.

Solis, D. R.; Fox, E. G. P.; Rossi, M. L.; Bueno, O. C. 2010. Description of the immatures of Linepithema humile Mayr (Hymenoptera: Formicidae). Biological Research 43:19-30.

Ward, P. S. 1987. Distribution of the introduced Argentine ant (Iridomyrmex humilis) in natural habitats of the lower Sacramento Valley and its effects on the indigenous ant fauna. Hilgardia 55(2):1-16. 

Wheeler, G. C.; Wheeler, J. 1951. The ant larvae of the subfamily Dolichoderinae. Proceedings of the Entomological Society of Washington 53: 169-210.

Wheeler, G. C.; Wheeler, J. 1990 ("1989"). Notes on ant larvae. Transactions of the American Entomological Society 115:457-473.

Wild, A. L. 2004. Taxonomy and distribution of the Argentine ant, Linepithema humile (Hymenoptera: Formicidae). Annals of the Entomological Society of America 97: 1204-1215.

Wild, A. L. 2007. Taxonomic revision of the ant genus Linepithema (Hymenoptera: Formicidae). University of California Publications in Entomology 126: 1-151.

Publication about Argentine and Odorous House Ants.
Layton, B. and J. A. MacGown. 2006. Control of Argentine Ants and Odorous House Ants in the Home.  Mississippi State University Extension Service, Publication no. 2407. 7 pp.

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