We know ants form large colonies. In 2002, we realized one specific kind of ant formed supercolonies. And then, in 2010, we learned that they had formed a global colony— and that, without even know it, we had helped them do it.
It’s not surprising that Argentine ants are a successful invasive species. Their major flaw is their inability to build large nests for themselves. If their colony gets too big they have to split up or find a nest abandoned by other ants. But once they get a home, they’re unstoppable. They can eat anything, from meat to sweets to vegetable oils. They are about three millimeters long and can fit through a single millimeter hole. They’re also highly aggressive toward other species of ant. Their home life, though, is relatively tranquil. Every colony supports multiple queens. Some estimate that ten percent of the Argentine ant population could be laying queens. Colonies spread through budding and sites that advise would-be ant farmers assure people that they can start a new colony with only a single queen and just a few workers. These things can go from twenty to twenty thousand with no problem.
Any invasive species gets some study. In the early 2000s, scientists studying the Argentine ant noticed something that didn’t add up: The ants did less fighting than they should. Different colonies of these territorial ants could meet, scavenge for food, or even come together and split apart, without recognizing each other as enemies. They behaved as if they were one supercolony.
This happened in different places around the world. California had a colony of ants—alternately called the Very Large Colony or the California Large—that stretched from northern California to the boundary of Mexico. At the border, the California Large was engaged in a war with another supercolony. Meanwhile, another supercolony had secured nearly four thousand miles of southern Europe.
Californian scientists took a look at the DNA of the Argentine ant, and found little variation. The ants were behaving like one colony because they were, genetically, one big colony, probably brought on by a population bottleneck. Over in Europe they decided to check out the ants’ behavior, staging over a thousand ant fights. By analyzing who was willing to attack whom, they realized that their continent belonged to only one or two supercolonies. This widespread fellowship, they decided, was because of the bounty of resources that the ants found when they got to a new environment. There was no reason to fight if there was enough food and nesting sites to go around.
It turns out that everyone was thinking too small. Argentine ants have formed supercolonies in Asia, Australia, New Zealand, Japan, Europe, and the Americas. Some of the supercolonies are smaller. Some are larger. Scientists decided to take at look at these ants both chemically and behaviorally. What they found was massive chemical overlap between the signals that the ants were giving off in the larger supercolonies.
When they put the ants in ant fights, ants that were separated by oceans, and thousands of generations, acted like they were in the same colony—but only if they were in the larger supercolonies. The representatives of the minor supercolonies and the major supercolonies still either fought or avoided each other. But when it came to the biggest colonies, as far as the ants were concerned they were all one colony.
Which might be why they managed to make a supercolony to begin with. By not snapping at their near-relatives just because they came from another continent, and by fighting everyone else, they could build a global empire. If they turned against us, could we do the same?