Because all the workers in an ant colony look the same, tracking their movements and interactions by eye is fiendishly difficult. Instead, Danielle Mersch and her colleagues tagged every single worker in entire colonies and used a computer to track them, accumulating what they say is the largest-ever data set on ant interactions. The biologists, based at the University of Lausanne in Switzerland, have found that the workers fall into three social groups that perform different roles: nursing the queen and young; cleaning the colony; and foraging for food. The different groups move around different parts of the nest, and the insects tend to graduate from one group to another as they age, the researchers write in a paper published today in Science1.
The team reared six colonies of carpenter ants (Camponotus fellah) in the lab and tagged each worker with paper containing a unique barcode-like symbol. The colonies — each comprising more than 100 ants — lived in flat enclosures filmed by overhead cameras. A computer automatically recognized the tags and recorded each individual’s position twice per second (see video below). Over 41 days, the researchers collected more than 2.4 billion readings and documented 9.4 million interactions between the workers. The researchers found that around 40% of the workers were nurses, which almost always stayed with the queen and her brood. Another 30% were foragers, which gathered most of the colony’s food and were found near the entrance to the nest. The rest were cleaners, and these were more likely to visit the colony’s rubbish heaps. The workers move between jobs as they get older — nurses are generally younger than cleaners, which are younger than foragers. Honeybees go through similar transitions from young nurses to older foragers, but this study provides the clearest evidence yet that ants do the same.