Argentine ants

Page last updated: Tuesday, 16 December 2014 - 3:57pm

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Argentine ants, Linepithema humile, are a major cosmopolitan pest ant species, primarily of the suburbs, which often enter houses in search of food and moisture.

They can also be a horticultural pest. This page describes ways to identify argentine ants, discusses their biology, and advises on effective control procedures. Control procedures outlined here are specific to argentine ants and may not be appropriate for other ant species. If you find your current ant control methods are unsuccessful you can send samples to the Department of Agriculture and Food, Western Australia.

Description

Argentine ants are very ordinary-looking, small brown ants. They are small and slender, 2.6 to 3.2mm long, and are dark brown in colour. The worker ants are uniform in shape and size and move in well defined trails. They have a slight greasy, musty odour when crushed. Argentine ants do not possess a sting but will bite readily, although the bite is not painful.

As the name suggests, argentine ants originate from South America and were first recorded in Western Australia (WA) in 1941 — initially in Albany and then in Perth. Argentine ants have also spread to many other regions of the world including the USA, South Africa and Europe, particularly between the 30°and 36° latitudes (north and south). The Department of Agriculture and Food, Western Australia (DAFWA), was involved in a long-running campaign to eradicate argentine ants in WA until 1988, when the campaign was terminated because of concerns with the broad-scale use of insecticides. Many new infestations have since been discovered in metropolitan Perth and also in country locations.

Biology

Argentine ants have a social structure in which there are numerous queens in each nest, and their nests are interconnected through an interchange of workers and queens. New colonies are formed by budding whereby one or more queens with attendant workers leave an existing nest and walk to a nearby location. While argentine ant queens do initially possess wings these are lost and new colonies are not established by queens flying to a new location. An entire infestation covering many hectares operates as a single colony with many nests.

Their food preference is the sugary honeydew produced by aphids, mealy bugs and scale insects. Heavy trails of argentine ants are often seen on the trunks of trees and shrubs. This is economically significant in horticulture as it encourages heavy populations of these plant pests to develop. Argentine ants feed on a wide variety of foods, including sweet drinks, cakes, pet food, meat and dead insects. The queens can live for several years, and compared to other ant species, individual workers are long-lived too, surviving for 10 to 12 months. These features contribute to argentine ant infestations maintaining high populations.

Symptoms

Continuous well-defined trails, sometimes more than three ants wide, of slow-moving, small brown ants of uniform size are often evidence of an argentine ant infestation. The ants will often readily climb onto a person’s hand when it is placed in their trail. Many other ant species will not do this.

Argentine ants are typically confined to urban areas and they nest outside buildings, at the base of trees or in the tree itself, along the edges of paths and in lawns and garden beds. They will thrive in swamps and low-lying areas where moisture is plentiful.

Populations peak from January to June, and they can be very invasive, coming indoors in large numbers in their search for food and moisture.

These ants are ecological pests. They attack nesting birds, hatching eggs and other native fauna. Argentine ants will quickly eliminate other ants from an infested area — especially native ants which play an important role in the ecosystem. They will rob commercial beehives and are significant pests in orchards and sometimes larger farms. There can be a significant cost to the community in their control, which is normally difficult, since it involves the ongoing and repetitive use of residual, contact insecticides.

Contact information

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080

Author

Marc Widmer