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Linepithema humile (Mayr)

Linepithema humile., full face view of worker.
Linepithema humile., profile view of worker with arrow pointing to petiole.
Linepithema humile, profile view of worker.

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.

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.

Workers of Linepithema humile are monomorphic and range in size from 2.2 to 2.6 mm in overall length. Like other ants in the subfamily Dolichoderinae, Argentine ants have only a single abdominal pedicel, the petiole; a 12 segmented antenna without club; a distinct promesonotal suture; a strong constriction between the mesonotum and propodeum; the lack of a sting or acidopore, instead having only a transverse slit-shaped cloacal opening; and a soft and flexible integument. Workers are usually a uniform light brown to brown; are slender bodied with an oval to somewhat triangular shaped head; have mandibles with two large apical teeth followed by a series of denticles; normally lack erect hairs on the alitrunk dorsum (as in the similar looking genus Forelius, which also has a different dental array on mandibles); and have an erect petiole (unlike Tapinoma sessile, a similar looking ant with the same type of dentition on mandibles, but without an erect node on petiole).

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. Argentine ants were considered to be one of the most persistant and troublesome of the house infesting ants by Marion Smith (1965).

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.

Argentine Ant Links:
AntWeb Images
Discover Life Images