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 paper is a game-changer, in the size and detail of the data set that was collected,” says Anna Dornhaus, an entomologist at the University of Arizona in Tucson. “Different methods of automatically tracking animal behaviour have recently been developed, and this is one of the first empirical studies that have come out as a result.”

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.