John Whitfield in The Guardian: It is a familiar story: a small group of animals living in a wooded grassland begin, against all odds, to populate Earth. At first, they occupy a specific ecological place in the landscape, kept in check by other species. Then something changes. The animals find a way to travel to new places. They learn to cope with unpredictability. They adapt to new kinds of food and shelter. They are clever. And they are aggressive.
People have long drawn comparisons between ant societies and human ones – but in fact they are a reminder of how limited our influence on the world really is
In the new places, the old limits are missing. As their population grows and their reach expands, the animals lay claim to more territories, reshaping the relationships in each new landscape by eliminating some species and nurturing others. Over time, they create the largest animal societies, in terms of numbers of individuals, that the planet has ever known. And at the borders of those societies, they fight the most destructive within-species conflicts, in terms of individual fatalities, that the planet has ever known.
This might sound like our story: the story of a hominin species, living in tropical Africa a few million years ago, becoming global. Instead, it is the story of a group of ant species, living in Central and South America a few hundred years ago, who spread across the planet by weaving themselves into European networks of exploration, trade, colonisation and war. Some even stowed away on the 16th-century Spanish galleons that carried silver across the Pacific from Acapulco to Manila. During the past four centuries, these animals have globalised their societies alongside our own.
It is tempting to look for parallels with human empires. Perhaps it is impossible not to see rhymes between the natural and human worlds, and as a science journalist I’ve contributed more than my share. But just because words rhyme, it doesn’t mean their definitions align. Global ant societies are not simply echoes of human struggles for power. They are something new in the world, existing at a scale we can measure but struggle to grasp: there are roughly 200,000 times more ants on our planet than the 100bn stars in the Milky Way.
In late 2022, colonies of the most notorious South American export, the red fire ant, were unexpectedly found in Europe for the first time, alongside a river estuary close to the Sicilian city of Syracuse. People were shocked when a total of 88 colonies were eventually located, but the appearance of the red fire ant in Europe shouldn’t be a surprise. It was entirely predictable: another ant species from the fire ants’ native habitats in South America had already found its way to Europe.
What is surprising is how poorly we still understand global ant societies: there is a science-fiction epic going on under our feet, an alien geopolitics being negotiated by the 20 quadrillion ants living on Earth today. It might seem like a familiar story, but the more time I spend with it, the less familiar it seems, and the more I want to resist relying on human analogies. Its characters are strange; its scales hard to conceive. Can we tell the story of global ant societies without simply retelling our own story?
ome animal societies hold together because their members recognise and remember one another when they interact. Relying on memory and experience in this way – in effect, trusting only friends – limits the size of groups to their members’ capacity to sustain personal relationships with one another. Ants, however, operate differently – they form what the ecologist Mark Moffett calls “anonymous societies”, in which individuals from the same species or group can be expected to accept and cooperate with each other even when they have never met before. What these societies depend on, Moffett writes, are “shared cues recognised by all its members”.
Ant under microscope: Image insert by despardes.com
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 nestmates 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 and red fire ant, 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 process, 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.
ll five of the ants included in the International Union for the Conservation of Nature’s (IUCN) list of 100 of the world’s worst invasive alien species are unicolonial. Three of these species – the aforementioned red fire ant, the Argentine ant and the little fire ant – are originally from Central and South America, where they are found sharing the same landscapes. It is likely that the first two species, at least, began their global expansion centuries ago on ships out of Buenos Aires. Some of these ocean journeys might have lasted longer than a single worker ant’s lifetime.
An ant formation–as they move along ‘peacefully’. Video insert by despardes.com
Unicolonial ants are superb and unfussy scavengers that can hunt animal prey, eat fruit or nectar, and tend insects such as aphids for the sugary honeydew they excrete. They are also adapted to living in regularly disrupted environments, such as river deltas prone to flooding (the ants either get above the waterline, by climbing a tree, for example, or gather into living rafts and float until it subsides). For these ants, disturbance is a kind of environmental reset during which territories have to be reclaimed. Nests – simple, shallow burrows – are abandoned and remade at short notice. If you were looking to design a species to invade cities, suburbs, farmland and any wild environment affected by humans, it would probably look like a unicolonial ant: a social generalist from an unpredictable, intensely competitive environment.
When these ants show up in other places, they can make their presence felt in spectacular fashion. An early example comes from the 1850s, when the big-headed ant, another species now listed on the IUCN’s Top 100, found its way from Africa to Funchal, Madeira’s capital. “You eat it in your puddings, vegetables and soups, and wash your hands in a decoction of it,” complained one British visitor in 1851. When the red fire ant, probably the best-known unicolonial species, spread through the US farming communities surrounding the port of Mobile, Alabama, in the 1930s, it wreaked havoc in different ways. “Some farmers who have heavily infested land are unable to hire sufficient help, and are forced to abandon land to the ants,” was how the entomologist EO Wilson described the outcome of their arrival. Today, the red fire ant does billions of dollars of damage each year and inflicts its agonising bite on millions of people. But the largest colonies, and most dramatic moments in the global spread of ant societies, belong to the Argentine ant.
