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Argentine ants

Argentine ants are not native to the United States.  They were introduced to the US probably on coffee ships from Brazil and Argentina through the port of New Orleans sometime before 1891. They spread rapidly on commercial shipments of plants and other materials.  Now Argentine ants are found throughout most of the southern states and California, with isolated infestations in a few other areas.

Argentine ant. Photo credit: Stanford Univ.Argentine ants have been very successful.  They are common in urban areas and can nest in diverse types of habitats. They can produce large numbers of offspring and survive on a wide variety of food. They often live on friendly terms with other neighboring colonies of the same species, but may eliminate some other ant species.

Identification

The workers which are all female are about 1/16" long and they are monomorphic, meaning they are all similar in size. Queens are twice as long or longer. Argentine ants are light to dark brown in color. They have a one-segmented petiole. The petiole is the segment between the thorax and the abdomen, and it can be one or two segments depending on the ant species. From the side, the thorax of this ant is uneven. While Argentine ants do not have stingers, they may bite when provoked. When these ants are crushed, they may give off a musty odor, but other ants may have an odor too. For example, odorous house ants, often confused with the Argentine ant, give off a sweet smell described as rotten coconuts when crushed.

Biology

Argentine ants form very large colonies of a few hundred to several hundred thousand workers. Each colony will have multiple queens, with the colony containing about 10% queens and 90% workers. The queen is usually an "egg-laying machine," and can lay thousands of eggs in one season. But unlike other species, the Argentine queen ant will actually help in the grooming and feeding of her young. Males are produced only when colonies are mature and die shortly after mating. The reproductives, those male and female ants with wings, do not leave the colony in a swarm to mate like other ant species.  They usually reach maturity in April or May and mate within the colony.  This protects the ants from harsh weather conditions and predators such as birds, frogs, lizards, and other insects.

New colonies are formed by one or more mated females migrating from the parent colony with a group of workers. Queens are unable to raise a brood alone.  In winter especially, several colonies may combine to form a larger colony in a favorable nesting site, then and divide again in spring or summer. 

Habits and Habitats

Argentine ant. Photo: Royal Forest and Bird Protection Soc. New ZealandArgentine ants are one of the trailing ants and may travel 200 feet or more with thousands of ants following each other from the nest to a food source. They prefer sweets and often tend honeydew producing insects. Their diet changes throughout the year. They feed on a number of items and are not considered "picky," since they are reported to feed on sweets, meats, fruits, dairy products, eggs, animal fats and waste, and vegetable oils. While the workers do not eat a lot, foods the ants have fed on may need to be discarded due to contamination because they also feed on garbage, sewage, dead animals and other items that may carry germs. 

Outdoors, Argentine ants can be found nesting in moist areas under debris (logs, concrete slabs, trash, and mulch) and in debris (rotten wood, faulty places in trees, refuse piles, bird nests, bee hives, and other places). They can form nests in exposed or covered soil. Argentine ants can form nests under homes and even within the home especially if their outdoor habitat is disrupted.

Indoors, Argentine ants crawl on or in every imaginable place such as stoves, refrigerators, shelves, beds, and clothing. Often looking for moisture, Argentine ants may be found on water pipes, dish washers or other wet locations.

Control

Argentine ants are one of the most persistent and troublesome of all the house-infesting ants.  A homeowner may have infestations year after year, unless control is very thorough. Complete control is achieved when all nests have been eliminated.

Some steps can be taken to lessen the chance of an Argentine ant invasion. Eliminate ground clutter such as piles of construction materials, boards, sheets of tin or plywood and even decaying plant material from the yard that could serve as protection.  Limit their access into the home by sealing cracks and crevices.  Minimize watering of lawns and flowerbeds which create moist conditions that are favorable for the ants.  Keep vegetation around the home to a minimum and trimmed away from the structure. Trim tree limbs in contact with the structure and electrical wires to remove an easy path for Argentine ants. Do not leave food, especially sweets, sitting on counter tops uncovered. 

Insecticides sprays or granules can be applied directly to the nests or around the structure. Make sure all nests are treated. To find ant nests, follow trails from the food source back to the nest.

Indoors, baiting is the preferred treatment for Argentine ants. Place baits at the closest point where ants are entering the structure. Make sure the ants are feeding on the bait.  Do not disturb or spray the ants in the bait stations. You must give the ants a few days to take the bait back to the colony to kill additional workers and the queens. Most ant baits can be found at many grocery and discount stores.  Follow all label directions for proper use of these baits.

In situations where the ant colonies are very large, a pest management professional may be needed. Pest control operators have access to application equipment and professional-use only products that can be quite effective in controlling Argentine ants when applied correctly.


Prepared by Jennifer S. Nauman, Graduate Extension Assistant, Patricia A. Zungoli, Extension Entomologist/Professor, and Eric P. Benson, Extension Entomologists/Professor, Department of Entomology, Soils, and Plant Sciences, Clemson University.
EIIS/HS-42 (New 04/2004).


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