Argentine ant

The Argentine ant, known scientifically as Linepithema humile, is a small insect with a massive global impact. These ants are tiny, measuring only 2.2 to 2.6 mm in length. They are usually a dull light to dark brown color.

While they are native to the riparian floodplains of South America, they have become one of the world's 100 worst invasive species. Humans have accidentally moved them across the globe. They now thrive in Mediterranean climates on almost every continent except Antarctica. This includes places like Japan, Australia, Europe, and the continental United States.

In their native lands, Argentine ants live in small, territorial colonies. However, in the new areas where they have been introduced, they behave very differently. Because their genetic makeup is so uniform, ants from different nests often do not recognize each other as enemies. Instead of fighting, they form massive groups called supercolonies.

These supercolonies can stretch across hundreds or even thousands of kilometers. One famous example is the Very Large Colony in California. This single population stretches from San Diego to beyond San Francisco. It may contain nearly one trillion individual ants.

Conflict does still happen when different supercolonies meet. When the borders of two massive groups clash, the fighting is constant and violent. Unlike other ants that might fight for a few hours, Argentine ants clash ceaselessly. In San Diego, scientists mapped the boundaries where different supercolonies fight. On the border between the Very Large Colony and the Lake Hodges Colony, thirty million ants die every year. These battles occur on a battlefront that covers many miles. These fights can sometimes be stopped by heavy rain or adverse weather.

Scientists have worked to understand how these ants recognize their own kind. One interesting factor is the role of diet in their identity. Researchers found that ants incorporate hydrocarbons, which are oily chemical compounds, from their food into their cuticle, or outer shell.

Ants that eat the same things appear to recognize each other as kin. If two groups eat completely different foods, such as flies versus grasshoppers, they develop different chemical cues. These groups then react violently toward one another. This suggests that what an ant eats helps shape its social identity.

History shows how our understanding of this species has evolved. An Austrian entomologist named Gustav L. Mayr first identified these ants in 1866. He found the first specimens near Buenos Aires, Argentina. Originally, the species was named Hypoclinea humilis. It was later moved to the genus Iridomyrmex. Finally, in the early 1990s, it was placed in the genus Linepithema. In 1913, researchers Newell and Barber were the first to report that separate colonies of these ants showed no apparent antagonism toward each other.

Argentine ants can disrupt entire ecosystems when they arrive in a new place. They often displace native ants, which causes a chain reaction. For instance, in southern California, the decline of coastal horned lizards is tied to these ants. The lizards lose their food source when Argentine ants push out the native ants the lizards eat. In South Africa, these ants affect plant life. They do not take seeds underground like native ants do. This leaves seeds on the surface, where they may fail to germinate. They also protect pests like aphids and mealybugs to feed on honeydew. This protection can cause problems for farmers in agricultural areas.

In urban settings, Argentine ants are common household pests. They enter buildings looking for food or water. They are especially active during hot, dry weather. They also move into homes to escape flooded nests.

Because colonies have many queens, they are difficult to control with standard sprays. Spraying can actually cause queens to lay even more eggs. Instead, people use slow-acting poison baits. These baits are carried back to the nest by workers to reach the queens. Researchers are even studying ways to use synthetic pheromones or the ants' own scents to disrupt their trails or control their populations.