Millions have died when humans went to war against each other ever since the dawn of humanity. While animals are known to have their own rivalries and great wars, one among ants, and at such intensity, is a first. In San Diego, a violent war between five rival ant supercolonies has been raging for decades, killing millions upon millions of them annually, as per a report by IFL Science.
Argentine ants: All over the world
The ants in question are Argentine ants, native to South America. The species (Linepithema humile) is highly territorial and prone to aggression towards other insects, using their antennae and chemical signalling to identify whether others are an outside foe or related friend.Throughout the 19th century, the species was accidentally spread across the world through trans-Atlantic shipping. Ants would hitch a ride on some cargo in South America, then find themselves planted across the world, from Europe to Japan. These different parts of the world were seeded by a small number of ants and their population was much less genetically diverse. They all “smelt” the same to each other, and thus nests treated each other as kin.As they stopped fighting and killing each other, many nests with their own queens merged into one huge cooperative “supercolony” spread across vast areas of land. Decades later, the supercolonies found themselves transplanted into yet another corner of the world, creating a battleground when they came into contact with other supercolonies that had strayed down their own path for generations.
A war in California
According to a 2006 paper published in the journal Molecular Ecology, southern California is home to five rival supercolonies of Argentine ants. The most dominant colony controls a 1,000-kilometre-long radius of loosely connected nests along the coasts of California, bordered by at least three of the four smaller colonies, each with their own town-sized enclaves.The scientists from UC San Diego explained that the miles-long borders between the territories were sharp, often divided by just a few metres. When the different groups of ants did come into contact, which they appeared to do regularly, violent clashes erupted.Fights between supercolonies were reported in 40% of the site visits by the researchers, averaging around 15,000 deaths per battle. Over months, the scale of death built up to shocking levels. The researchers estimated that at least 15 million worker ants died in a single border skirmish around one of the smaller colonies near Lake Hodges in north San Diego, over their six-month study.
No end in sight
What’s remarkable is that the borders barely moved over the months of the research. They might have shifted back and forth from week to week, but neither side was steadily on winning grounds. The supercolonies were stuck in a war that went on forever, losing massive amounts of life but gaining no new territory.What has shocked the researchers is the similarity between this warfare and that among humans. The stalemate has a striking resemblance to the Western Front of the First World War, where the Allied and Central Powers dug into trenches and ground each other down, with the front line barely moving over the course of years. However, unlike the soldiers of World War I, the supercolony stalemate might not have an end.Writing for Scientific American in 2011, biologist Mark W. Moffett explained that Argentine ants are unusual because they don’t show the “dear enemy effect,” in which territorial animals become less aggressive toward familiar neighbouring rivals than toward unfamiliar strangers after long bouts of violence. Through this effect, a kind of demilitarised zone can eventually emerge along the boundaries where violence does not occur. Under the right circumstances, the two territories can break away from each other, and the killing stops.However, Moffett argued that Argentine ants do not have this privilege. In their native South America, the species will often battle it out over floodplains. Rival colonies will often battle, but the fighting will stop each time the waters rise. The conflict never resolves, so they’re programmed to just keep going, and going, and going.