The Society That Cannot Recognise

In 2002, three researchers at Lausanne — Tatiana Giraud, Jes Pedersen and Laurent Keller — sampled Argentine ants from thirty-three populations along the coasts of Italy, France, Spain and Portugal, and then put workers from every possible pairing of those populations together to see what happened. Over eleven hundred trials, scored on a scale from ignores the other to fights to the death.

The result was that across some six thousand kilometres of coastline, aggression never occurred within the main supercolony. Ants that were separated by a distance no individual ant could cross in a hundred lifetimes antennated each other briefly and got on with it. The authors called it the largest cooperative unit ever recorded.

What makes this interesting is not tolerance. These ants are not peaceable. In the same study, workers from the main supercolony were paired with workers from Europe’s other supercolony — a much smaller one in Catalonia, on the Spanish east coast — and in ninety-eight per cent of those trials an ant died. Later work took the test intercontinental: ants from the large supercolonies on different continents did not fight each other either.

So the discrimination does not track anything we would expect it to track — not distance, not acquaintance, not shared food. Ants from different supercolonies keep killing each other after months on identical diets.

The mechanism is a smell. Each ant carries a profile of hydrocarbons on its cuticle, and that profile is largely genetically determined rather than acquired — which is why it stays uniform across a range no ant traverses. The chemical distance between populations predicts the aggression: measure the profiles, and you can predict the fights.

Here is where Mark Moffett comes in, and where a biological finding turns into an argument about a word. In a 2012 paper in Behavioral Ecology titled, plainly, “Supercolonies of billions in an invasive ant: What is a society?”, he argued that the supercolony is a single society — and that our reluctance to say so reveals an assumption we did not know we were making.

His definition: a society is a cooperative group whose members can distinguish members from outsiders and reject outsiders on that basis. Nothing about interaction. Nothing about proximity, or acquaintance, or a member ever encountering another. Distance is not a membership criterion, so distance cannot break the society. He calls these anonymous societies, and contrasts them with the small individual-recognition societies most vertebrates run — dolphins, elephants, chimpanzees.

The paper was published as a forum piece with commentaries. Deborah Gordon, who has studied Argentine ants in California for years, and Nicole Heller hold that there is no functional supercolony at all — that the real units are nest clusters, defined by where ants and food actually travel, and that calling the whole range one colony describes a genetic relationship rather than a society. Philip Lester and Monica Gruber sided with them, and attacked Moffett’s population threshold as unworkable: you cannot count ants. Andrew Suarez and Erin Suhr accepted the supercolony but rejected the numbers, since some single-nest species exceed a million workers too.

What I find worth keeping is not a verdict on the ants. It is the shape of the disagreement. Nobody disputes the behaviour. Gordon does not think the ants fight when Moffett says they do not. The disagreement is entirely about whether non-aggression plus a shared badge is enough to be called one society, when ants and food do not travel across the range.

That is a disagreement about a word, conducted by people who agree about the facts. The word has to be settled before the question can even be asked. Moffett’s definition makes the supercolony one society; Gordon’s makes it many. Both are coherent, and each licenses different research.

It would have happened had he not asked. Moffett put the question in the title of a paper — what is a society? — and made his colleagues answer it, which they did. The question, asked and answered where it could be argued rather than assumed.

This post is part of the conversations series. See also the reference entry on Mark Moffett.

Photo: juanmascan1978 / Unsplash