Ant geopolitics

From the article:

Recognition looks very different for humans and insects. Human society relies on networks of reciprocity and reputation, underpinned by language and culture. Social insects – ants, wasps, bees and termites – rely on chemical badges of identity. In ants, this badge is a blend of waxy compounds that coat the body, keeping the exoskeleton watertight and clean. The chemicals in this waxy blend, and their relative strengths, are genetically determined and variable. This means that a newborn ant can quickly learn to distinguish between nest mates and outsiders as it becomes sensitive to its colony’s unique scent. Insects carrying the right scent are fed, groomed and defended; those with the wrong one are rejected or fought.

The most successful invasive ants, including the tropical fire ant (Solenopsis geminata) and red fire ant (S invicta), share this quality. They also share social and reproductive traits. Individual nests can contain many queens (in contrast to species with one queen per nest) who mate inside their home burrows. In single-queen species, newborn queens leave the nest before mating, but in unicolonial species, mated queens will sometimes leave their nest on foot with a group of workers to set up a new nest nearby. Through this budding, a network of allied and interconnected colonies begins to grow.

In their native ranges, these multi-nest colonies can grow to a few hundred metres across, limited by physical barriers or other ant colonies. This turns the landscape to a patchwork of separate groups, with each chemically distinct society fighting or avoiding others at their borders. Species and colonies coexist, without any prevailing over the others. However, for the ‘anonymous societies’ of unicolonial ants, as they’re known, transporting a small number of queens and workers to a new place can cause the relatively stable arrangement of groups to break down. As new nests are created, colonies bud and spread without ever drawing boundaries because workers treat all others of their own kind as allies. What was once a patchwork of complex relationships becomes a simplified, and unified, social system. The relative genetic homogeneity of the small founder population, replicated across a growing network of nests, ensures that members of unicolonial species tolerate each other. Spared the cost of fighting one another, these ants can live in denser populations, spreading across the land as a plant might, and turning their energies to capturing food and competing with other species. Chemical badges keep unicolonial ant societies together, but also allow those societies to rapidly expand.

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In the past 150 years, the Argentine ant has spread to pretty much everywhere that has hot, dry summers and cool, wet winters. A single supercolony, possibly descended from as few as half a dozen queens, now stretches along 6,000 kilometres of coastline in southern Europe. Another runs most of the length of California. The species has arrived in South Africa, Australia, New Zealand and Japan, and even reached Easter Island in the Pacific and St Helena in the Atlantic. Its allegiances span oceans: workers from different continents, across millions of nests containing trillions of individuals, will accept each other as readily as if they had been born in the same nest. Workers of the world united, indeed. But not completely united.

Expanding in parallel with the world-spanning supercolony are separate groups of the Argentine ant that bear different chemical badges – the legacy of other journeys from the homeland. Same species, different ‘smells’. In places where these distinct colonies come into contact, hostilities resume.

In Spain, one such colony holds a stretch of the coast of Catalonia. In Japan, four mutually hostile groups fight it out around the port city of Kobe. The best-studied conflict zone is in southern California, a little north of San Diego, where the Very Large Colony, as the state-spanning group is known, shares a border with a separate group called the Lake Hodges colony, with a territory measuring just 30 kilometres around. Monitoring this border for a six-month period between April and September 2004, a team of researchers estimated that 15 million ants died on a frontline a few centimetres wide and several kilometres long. There were times when each group seemed to gain ground, but over longer periods stalemate was the rule. Those seeking to control ant populations believe provoking similar conflicts might be a way to weaken invasive ants’ dominance. There are also hopes, for example, that artificial pheromones – chemical misinformation, in other words – might cause colony mates to turn on one another, although no products have yet come to market.