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Subfamily DOLICHODERINAE
Tribe DOLICHODERINI

Linepithema humile (Mayr, 1868)
"Argentine ant"

Authors: Joe A. MacGown and Ryan J. Whitehouse
Uploaded 2008; last updated 11 October 2016

Linepithema humile, full face view of a worker (MS, Jackson Co.) (photo by Joe A. MacGown)
Linepithema humile, lateral view of a worker (MS, Jackson Co.) (photo by Joe A. MacGown)
Linepithema humile, dorsal view of a worker (MS, Jackson Co.) (photo by Joe A. MacGown)
Linepithema humile, full face view of a queen (MS, Jackson Co.) (photo by Joe A. MacGown)
Linepithema humile, lateral view of a queen (MS, Jackson Co.) (photo by Joe A. MacGown)
Linepithema humile, lateral view of a male (MS, Jackson Co.) (photo by Joe A. MacGown)
Linepithema humile, full face view of a male (MS, Lauderdale Co.) (photo by Joe A. MacGown)
Linepithema humile, lateral view of a male (MS, Lauderdale Co.) (photo by Joe A. MacGown)
Linepithema humile, dorsal view of a male (MS, Lauderdale Co.) (photo by Joe A. MacGown)
Linepithema humile., lateral view of worker (photo by Joe A. MacGown)
Linepithema humile, lateral view of worker (photo by Joe A. MacGown)
Linepithema humile., profile view of worker with arrow pointing to petiolar node.

Linepithema humile, lateral view of worker (drawing by Joe MacGown). Arrow points to
the single pointed node between the propodeum and the gaster. Scale bar equals 2 mm.

Introduction
Linepithema
 humile, the Argentine ant, is an introduced ant native to Argentina and Brazil. The Argentine ant is thought to have first arrived in the United States in coffee shipments in 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.

The genus Linepithema can be identified by its lack of a sting or acidopore; erect node; lack of spine or other topographical modifications on the propodeum and its triangular mandibles that are longer than the clypeal setae.

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: HL 0.70-0.76mm, HW 0.61-0.69mm, SL 0.73-0.75mm, EL 0.19-0.20mm, MeSL 1.00-1.07mm (n=5) (MEM specimens). Brown monomorphic ants that are generally uniformly colored, but some specimens have their heads and gasters darker than the mesosoma. Workers range in size from 2.2-2.6 mm in overall length. Head smooth and 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 are 12-segmented and lacking a club. Mesosoma is smooth with dense, short, appressed setae; distinct promesonotal suture; in profile the mesosoma is relatively flat with no distinct sculpturing or teeth; propodeal declivity smooth; propodeum unarmed. Waist is 1-segmented; petiolar node thin. Gaster somewhat shiny with dense, short, appressed setae; does not project over the petiole; sting or acidopore not present.

Queen: HL 0.91-0.99mm, HW 0.88-0.96mm, SL 0.91-0.94mm, EL 0.40-0.42mm, MeSL 2.16-2.42mm (n=5) (MEM specimens). Reddish-brown to dark brown ant that is generally uniformly colored. Head smooth and shinning with dense, appressed setae that is less dense than in the workers; eyes large, about 1/3 the length of the head, located in front of the midpoint of the head; three ocelli present; mandibles triangular and multidentate; clypeus with 2-6 setae that are shorter than the closed mandibles; antennae are 12-segmented and lacking a club. Mesosoma smooth and shinning with dense, short, appressed setae; four wings or wing scars present; dorsum smooth and even; propodeum is unarmed. Waist is 1-segmented; petiolar node thin. Gaster is shining with dense, short, appressed setae; anterior face with slight declivity where it meets the petiolar node; does not overhang the petiole; apex without a sting or acidopore.

Male: HL 0.64-0.67mm, HW 0.66-0.69mm, SL 0.18-0.19mm, EL 0.34-0.38mm, MeSL 1.59-1.76mm (n=5) (MEM specimens). Brown to dark brown ants with the head and gaster darker than the rest of the body, sometimes almost black. Head almost rectangular with dense, appressed setae; eyes large, about half the length of the head, and located on the front half of the head; three large ocelli present; mandibles small and poorly developed; when closed, the mandibles form a smooth arc; antennae 13-segmented; antennal scape short with the third antenomere equal in length or longer; last 8 antenomeres small compared to the rest of the antenomeres. Mesosoma shining with dense, appressed setae; enlarged with four wings present; enlarged bump between the wings, before the propodeum; propodeal declivity almost vertical. Waist is 1-segmented; petiolar node short, about as tall as the width of the base. Gaster shining with dense, short setae; does not overhang petiole.

Workers of Linepithema humile can be separated other ant species in the area by their lack of a sting or acidopore at the apex of the gaster and their 12-segmented antennae lacking a club. Linepithema humile can be separated from the similar genus Forelius by their 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 shaped when closed and have long clypeal setae that extend past the mandible when they are closed. Linepithema humile can also be separated from Tapinoma species by their erect petiolar node (Tapinoma species lack an erect petiolar node).

Biology and Economic Importance
The Argentine ant has established itself as a major pest in this country because of its ability to nest in many diverse habitats, its production of uncountable numbers of individuals 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 everywhere else. 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).

Linepithema humile’s ability to nest in such a wide range of habitats and feed on such a wide variety of food makes them the perfect house pest. Once infesting a house, they will stick around for a long time and are extremely difficult to get rid of (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). Argentine ants also tend to have a large ecological impact exterminating other ant species in their area. They are known to be especially competitive with Solenopsis xyloni, 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 Bullitin 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.

Links:
AntCat
AntWeb
AntWiki