Lois Swoboda, Graduate Student, Virginia Tech
Dini Miller, Professor, Virginia Tech
Species: Linepithema humile (Mayr)
Not known to be established in Virginia.
Argentine ants are approximately 1/8” (2-3 mm). They are light to dark brown. Their abdomen may appear silvery after heavy feeding.
Argentine ants are small ants. They are often present in great numbers and may form long lines. They forage 24 hours a day. Workers are all one size although a larger queen may occasionally be seen foraging in the open. Queens are 2 to 4 times larger than workers and are grayish brown in color. Winged males may also be present in lines of foragers. Argentine ants are identified by the following characteristics:
* The thorax lacks spines.
* The pedicel is a single segment and visible when the ant is viewed from above.
* Argentine ants produce a faint grease-like odor when crushed.
The Argentine ant is now permanently established in California and parts of the southern United States, including Georgia and Florida. Argentine ants are not firmly established in Virginia but spotty transient infestations have been reported. It is believed that these ants have been transported to Virginia in landscape materials and houseplants arriving from further south. These ants are most commonly encountered in urban areas and along the coast. Argentine ants are usually found on trees or shrubs, in flowerbeds, in and around mulch, and in trash heaps. In the summer, these ants live in shallow nests under mulch, refuse, or the roots of a tree or shrub. Occasionally, Argentine ants actually nest on the surface of the soil. In cold weather, they withdraw into deeper central nests, foraging whenever the weather allows. Argentine ants prefer to nest outdoors but, in areas outside their normal range, they will sometimes nest in structures, frequently in hollow areas of plumbing fixtures or in houseplants.
Argentine ants live in supercolonies,
nests that may contain hundreds of
queens and millions of workers and
may cover several city blocks. During
cold weather, the ratio of workers to
queens is much lower than in summer
months. Like all ant, this species has
a complex life cycle developing from
eggs into white legless larvae and pupae
before emerging as adults. Development
from egg to pupa takes place within the
nest and immatures are rarely seen.
Queens and drones mate within the
nest. Only the drones emerge and fly away, where they will probably die without mating again. Swarms of males occur between dusk and dawn and are rarely seen. When queens disperse, it is on foot, and they are accompanied by an escort of workers and sometimes brood.
Argentine ants are nuisance pests in and
around structures because they are usually
present in great numbers. They do not sting
and their bite is barely noticeable.
These ants may “cultivate” aphids, scale
insects, or mealybugs on fruit trees, house-
plants, or ornamental plantings. These
sucking insects produce a sweet excretion
called honeydew that Argentine ants use for
food. Argentine ants also feed on the
honeydew-producing insects themselves.
Infestations of mealybugs, aphids, and other
sucking pests can damage the health of the
affected plant or cause it to become unsightly.
Because Argentine ants will harass natural
predators to protect their “livestock”, they frequently interfere with integrated pest management programs involving biological control, which is the use of a natural enemy to control a pest organism. This ant is an important agricultural pest in citrus orchards and vineyards. Argentine ants will also attck and destroy hives of domesticated honeybees.
In addition, Argentine ants are a serious threat to the ecosystem. They may east nestling birds. They outcompete native insects for food and habitat, and consume or displace natural predators such as lizards, snakes, and spiders.
Inside: Reduce available moisture whenever possible. Store food in well-sealed containers. Kitchen counters and drains should be kept free of potential food and wiped frequently with water containing lemon juice or ammonia. Windowsills and sliding glass doors may also be potential sources of food for these ants since they are frequently littered with the bodies of dead insects, which can be trapped while attempting to escape from a structure. These areas must also be kept free of refuse and frequently wiped clean.
Outside: Trim trees and shrubs to prevent contact with buildings because ants may use them as bridges to gain entry into buildings. Landscape plants that are chronically infested with the honeydew-producing insects should be treated for the infestation or removed entirely. Chalk dust lightly applied to tree trunks with a duster or shaker will discourage infestation by this ant.
Sugar-based baits containing 1 percent of less boric acid or baits containing 1 percent or less sulfuramid are often well accepted by this ant. Baits with a higher concentration of active ingredient are usually refused. DO NOT attempt to spray these ants. Sudden disruption of the nest due to spraying or other factors can cause nests to split and worsen the infestation. Perimeter sprays with repellant insecticides like pyrethroids are also inadvisable since ant colonies nesting under a structure and foraging outside may become trapped and forced to move their foraging activities into the building.
This ant probably first arrived in the U.S. at the Port of New Orleans in the 1890s. It is believed to have traveled on coffe boats from Brazil, not Argentina. It was originally known as the New Orleans ant but the city leaders objected and the name was changed.
Copyright M. Stedfast 2014