Argentine Ant

The Argentine ant is a small, unassuming species native to the floodplains of the Parana River in Argentina, Brazil, Paraguay, and Uruguay. Since the late 1800s it has spread to mild-climate regions worldwide, including coastal California, the Mediterranean, South Africa, Japan, and Australia, largely through the movement of agricultural goods and nursery plants.

What makes this species remarkable is its unusual social structure. Unlike most ants, introduced Argentine ant populations lack the genetic diversity that normally causes colonies to recognize and fight rival nests. As a result, ants from thousands of separate nests treat one another as nestmates, merging into vast unicolonial "supercolonies" that can extend for many kilometers and contain millions of interconnected workers and queens.

This cooperative structure gives Argentine ants a strong competitive advantage over native ant species, and they are considered one of the world's most successful invasive insects, frequently displacing native ants in the areas they colonize.

• Small, monomorphic (uniform-sized) worker ants roughly 2-3 mm long
• Light to dark brown coloring, sometimes with a faint sheen
• One node on the petiole (waist), not visible from above
• No stinger; releases a musty, somewhat rotten odor when crushed
• Moves in dense, well-defined foraging trails along edges, wires, and plant stems
• Lacks the erratic zig-zag running of crazy ants and is smaller and less shiny than carpenter or field ants

In its native range, this species inhabits floodplain forests and disturbed ground along South American rivers. Introduced populations favor mild, moist climates and are especially common in irrigated landscapes such as suburban lawns, gardens, orchards, and vineyards. Colonies nest in shallow soil, under mulch, pavement, or debris, and readily relocate nest sites in response to moisture changes, often moving indoors during hot, dry spells or heavy rain.

Argentine ants are omnivorous generalists, feeding on other insects, seeds, and sugary substances. They are especially attracted to honeydew produced by aphids, scale insects, and mealybugs, which they tend and protect in a mutualistic relationship, sometimes increasing pest insect populations on plants as a side effect. Their supercolony structure allows extremely high worker densities and near-continuous foraging trails rather than the aggressive, spaced-out territories typical of most ant species. Because they rarely fight rival colonies, they can out-forage and outcompete native ants for food and nesting space.

Like all ants, Argentine ants undergo complete metamorphosis: egg, larva, pupa, and adult. Colonies are highly polygynous, containing many egg-laying queens rather than a single one. New colonies form primarily through budding, in which a queen and a group of workers split off to found a satellite nest nearby, rather than through dramatic winged mating flights. In mild climates, brood production and colony growth continue nearly year-round, slowing only during cooler winter months.