Ants change their careers

Worker ants change job as they age, a new study has found.
Biologists tagged every worker in six colonies and used a computer to track their movements.
A photograph was taken every half a second over a period of six weeks and from this the scientists found that the workers fell into three separate social groups.
The ants that nursed the queen and the young tended to be young, slightly older ants were responsible for cleaning the colony and the third group of ants, usually the oldest, foraged for food outside the colony.
The six-year project by scientists at the University of Lausanne in Switzerland, accumulated the largest ever data of ant interactions.
Professor Laurent Keller said: “It was a very challenging task to tag all the ants. We pasted code bars on to each of them and a picture was taken every half a second.
“The life expectancy of an ant is about one year and we knew the age of every single ant.
“We found that around a third of the workers were nurses, which almost always stayed with the queen and eggs. Another third were cleaners and the rest were foragers, collecting food outside the colony.
“We also found that they tend to graduate from one group to another as they age, although the career changes were not clear-cut. We did find very old nurses and young foragers.
“We also found that the ants interacted mostly with workers from the same group. They don't try to interact with workers from another group.”
Even if the colony's entrance and brood chamber were close together, the study showed that nurses and foragers stick to their own company and seldom mix.
The team reared six colonies of carpenter ants and tagged each worker with a unique barcode.
The colonies – comprising about 150 ants – lived in flat enclosures and were filmed by overhead cameras.
A computer recognised the tags and recorded each individual's position twice a second. It is not yet clear how they know when and how to adapt, but the study's findings suggest there is now evidence to show they communicate using hormones and their antenna.
Honeybees go through similar transitions from young nurses to older foragers, but this study provides the clearest evidence yet that ants do the same.
Professor Keller said: 'Like bees, we have now shown that ants' behaviour changes with age.”