The borders where Argentine ant supercolonies collide
A California study found intense fighting between enormous ant societies. Its striking mortality estimate came from sampled borders and an explicit extrapolation.
Argentine ants can tolerate neighbors from nests hundreds of miles apart while fiercely attacking ants just across a territorial boundary. A UC San Diego-led study published in 2006 documented that contrast in southern California, where vast supercolonies met along sharply defended borders. [1]
A supercolony is more than one nest
In a supercolony, ants from many different nests show little or no aggression toward one another. UC San Diego’s account of the research described five known southern California supercolonies, with the largest extending roughly 600 miles along coastal California. That historical estimate describes the study’s setting, rather than a newly surveyed boundary map. [1]
Size did not mean universal peace. The largest supercolony bordered several smaller ones, including a colony around Lake Hodges, north of San Diego. Ants from distant parts of the same supercolony could meet without fighting, while workers from rival supercolonies fought intensely where their territories touched. Membership mattered more than simple proximity. [1]
What the researchers actually counted
Melissa Thomas and colleagues monitored 16 contact zones from April through September 2004, visiting nine weekly. They found persistent territorial conflict, although its intensity varied. Borders shifted locally but generally showed little net movement across the observation period. [2]
The widely repeated figure of more than 15 million dead workers was an extrapolation, not a count of 15 million individual bodies. The paper estimated the Lake Hodges colony’s circumference at about 30.5 kilometers. If even one-quarter of that border contacted the surrounding large supercolony, the sampled mortality implied more than 15 million deaths over six months. [2]
Why the boundary mattered
Genetic tests found stronger differentiation across supercolony borders than within them, and aggression was correlated with genetic differentiation rather than geographic distance. This supported the role of inherited recognition differences; it did not mean ants consciously read one another’s DNA. [2]
The results challenged the idea that California’s conditions removed territorial aggression. Cooperation within supercolonies coexisted with boundary defense. These observations do not establish that the same borders or battles persist today. [2]
The consequences reach beyond the fighting
Argentine ants are also an invasive species with effects on surrounding ecosystems. UC Riverside’s Center for Invasive Species Research describes their ability to displace native ants and disrupt food webs. Their success therefore matters beyond the dramatic clashes between supercolonies of their own species. [3]
Food relationships help explain their impact. In citrus orchards, the ants tend honeydew-producing insects and protect them from natural enemies in return for sugary food, according to UC Riverside’s biological-control researchers. That cooperation can benefit plant-feeding pests. The supercolony story is consequently about both conflict and cooperation, with consequences for insects and plants sharing the same habitat. [4]
Story context and image credits
Study observations: April–September 2004; research published 2006. Original Instagram publication: 2026-10-11T12:40:01.000Z; 1 Reel. Expanded website article added October 13, 2026.
View the full photo-credit recordView the original Instagram publicationSources & notes
- UC Riverside Applied Biological Control Research: Argentine Antsbiocontrol.ucr.edu
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