The Argentine ant, Linepithema humile, originates from the Paraná River drainage basin in South America, from parts of Argentina, Uruguay, Paraguay, and southern Brazil. This small, dull brown species has become a globally widespread invasive pest, particularly in regions with Mediterranean-type climates, including California, Europe, and Australia. The success of Argentine ants as an invasive species is tied to their queens’ unique biology and behavior. Unlike many ant species, their reproductive strategies and social organization enable the formation of immense, interconnected colonies that can dominate new environments.
Reproduction and Colony Formation
Argentine ant queens do not undertake typical “nuptial flights” where winged queens fly to mate and establish new colonies alone. Mating occurs within the parent nest between winged reproductive males and females. This internal mating reduces the exposure of new reproductives to predators, contributing to their survival.
New Argentine ant colonies are primarily formed through a process called “budding.” During budding, one or more mated queens, accompanied by workers, walk away from the existing nest to establish a new satellite nest nearby. This method allows for rapid colony expansion, differing from the solitary founding common to many ant species.
Life Inside a Multi-Queen Colony
Argentine ant colonies exhibit polygyny, meaning they contain multiple egg-laying queens within a single nest. A typical nest can house many queens, sometimes hundreds. This contrasts with the monogynous structure of most ant species, where a single queen is responsible for all reproduction.
These numerous queens maintain high egg production, fueling rapid colony growth. While there can be reproductive competition among queens, leading to some queens laying more eggs than others, the collective output ensures a steady supply of new workers and reproductives. This high reproductive capacity allows colonies to quickly increase numbers and spread.
The Architects of a Supercolony
The unique reproductive strategy of budding and multiple queens lays the groundwork for massive “supercolonies.” A defining characteristic of supercolonies is the lack of aggression between ants from different, often distant, nests. This unusual tolerance allows individual nests to link up, creating vast, cooperative networks that can span enormous areas.
For example, a notable supercolony in California extends from San Diego northwards beyond San Francisco, covering hundreds of kilometers. Another immense supercolony stretches approximately 6,000 kilometers along the Mediterranean coast, from northwestern Iberia through France to Italy, potentially comprising billions of workers and tens of millions of queens. Ants within these supercolonies recognize each other as kin, even across vast distances and after prolonged separation.
Why Eradicating Argentine Ant Colonies is Difficult
The multi-queen, interconnected nest structure of Argentine ants presents challenges for eradication. Simply killing individual workers or even a single queen has minimal impact on the overall colony’s survival because many other queens can continue to lay eggs. Some colonies may have as many as 15 queens for every 1,000 workers, making it impractical to target each queen individually.
Physical disturbance of a nest can trigger further budding, causing ants to disperse and establish new nests, potentially worsening an infestation. Effective control strategies must therefore account for this unique biology. Targeting the entire hidden network of nests and queens, often through slow-acting baits workers carry back to the colony, is required for lasting management rather than just addressing visible ant trails.