Argentine ants are native to central South America but have spread to six continents, making them one of the most widespread invasive insects on Earth. They thrive in Mediterranean and subtropical climates and are now firmly established across southern Europe, coastal California, parts of Australia, New Zealand, South Africa, Japan, and many other temperate regions. At a local level, they nest in moist soil, under rocks, at the base of trees, inside wall voids, and near any reliable water source.
Their Native and Global Range
Argentine ants originated in the river basins of central South America, primarily in northern Argentina, Uruguay, Paraguay, and southern Brazil. From there, likely hitching rides on commercial shipping in the late 1800s, they colonized every continent except Antarctica. The Global Invasive Species Database lists confirmed populations in the United States, Mexico, Chile, Peru, Cuba, Bermuda, Spain, Portugal, France, Italy, Switzerland, the United Kingdom, South Africa, the United Arab Emirates, Japan, Australia, and New Zealand.
In the United States, they are most abundant along the California coast and throughout the Southeast. Southern California is a hotspot: the mild, irrigated landscape provides near-perfect conditions. They’re also well established in states like Louisiana, Georgia, and the Carolinas, where warm, humid summers support large colonies.
The Supercolony System
What makes Argentine ants unusual is the scale at which they organize. Instead of forming small, independent colonies that compete with one another, introduced populations merge into supercolonies containing billions of workers spread across enormous distances. In California, a single supercolony stretches at least 900 kilometers. In New Zealand, one spans 700 kilometers. The largest known supercolony runs more than 4,000 kilometers through Spain, Portugal, France, and Italy.
Even more remarkably, behavioral tests have shown that workers from the dominant supercolonies on different continents treat each other as nestmates. Researchers paired ants from California, Japan, Europe, New Zealand, and Australia and observed zero aggression in dozens of trials. This means these far-flung populations function as a single, planet-spanning society, likely the most populous animal society ever documented. The leading explanation is that constant human-assisted movement of ants between regions keeps the populations genetically similar enough to recognize one another.
Outdoor Nesting Preferences
Argentine ants shift their nesting sites with the seasons to maintain the right temperature and moisture. During cold, rainy months they nest primarily underneath rocks, where the stone absorbs and retains heat. In warmer periods they relocate to the bases of trees. Even small-scale terrain features like slope angle and sun exposure influence which rocks they choose.
In the southeastern United States, winter nests cluster around loblolly pines. The evergreen canopy provides warmer bark temperatures than nearby deciduous trees, and the ants can forage on the trunk even on cold days. Deciduous trees, stripped of leaves and food sources, are ignored. When researchers experimentally added sugar water to bare deciduous trees during winter, the ants promptly moved in and nested at the base, confirming that both warmth and food drive their site selection.
Why Water Controls Where They Live
More than almost any other factor, soil moisture determines whether Argentine ants can occupy a given area. A field experiment at UC San Diego demonstrated this directly: when researchers irrigated normally dry land with drip lines for six months during Southern California’s dry season, the number of Argentine ant nests increased 54 percent within three months. When irrigation stopped, the ants gradually retreated, returning to pre-irrigation levels after another three months.
This is why Argentine ants are such a persistent problem in irrigated suburbs surrounded by otherwise arid landscape. Lawns, garden beds, and leaky sprinkler systems create artificial oases. If you live in a dry climate and deal with Argentine ant invasions, reducing outdoor irrigation is one of the most effective things you can do. The researchers found that plant cover alone provided only a small boost to ant populations compared with water, confirming that moisture, not vegetation, is the primary draw.
Where They Nest Inside Homes
Argentine ants enter buildings in search of water and food, especially during dry or very hot weather when outdoor conditions become inhospitable. Inside, they nest in wall voids, beneath flooring, and near any plumbing that provides consistent moisture. Leaking pipes under a kitchen sink or a bathroom with poor ventilation can sustain an indoor colony indefinitely. They don’t excavate wood like carpenter ants; they simply occupy existing gaps and cavities close to water.
Because their supercolony structure means there are no territorial boundaries between nearby nests, trails of Argentine ants moving into a house can draw from an enormous outdoor population. A single visible trail may connect to thousands of nests across your neighborhood.
Temperature Limits on Survival
Argentine ants reproduce best in a narrow temperature window. The optimal temperature for egg-laying and brood survival is around 26 to 28°C (roughly 79 to 82°F). At 32°C (90°F), no eggs survive at all. At 18°C (64°F), fewer than 2 percent of eggs hatch. Larvae are more cold-sensitive than eggs: only about 19 percent of larvae survive to the next stage at 21°C, compared with 94 percent at 30°C. Pupae, on the other hand, survive at 100 percent regardless of temperature in tested ranges.
Workers can forage across a broader range, staying active in temperatures from roughly 5 to 15°C on the low end up to 30 to 34°C on the high end. Beyond those thresholds, activity drops sharply. This is why Argentine ants dominate in mild, Mediterranean-type climates and struggle in places with extreme cold or sustained heat above 32°C. Harsh winters and truly arid deserts remain natural barriers to their spread.
How They Reshape Local Ecosystems
Wherever Argentine ants establish, native ant species tend to disappear. Their competitive advantage comes from sheer numbers: they recruit massive groups of workers to food sources and overwhelm other species through both direct fighting and simply monopolizing resources. In Mediterranean citrus orchards, they’ve become a common agricultural pest, partly because they protect sap-feeding insects like aphids and scale bugs in exchange for the sugary honeydew those insects produce. This mutualism boosts both the ant population and the crop damage caused by the sap feeders.
The displacement of native ants has cascading effects. Native ants disperse seeds, aerate soil, and serve as food for lizards, birds, and other predators that often won’t eat Argentine ants. In parts of coastal California, the decline of native harvester ants after Argentine ant invasion has been linked to reduced food availability for the threatened coast horned lizard, which depends almost entirely on harvester ants for its diet.