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How does an ant decide what to do?

Posted by on July 12, 2012

Black garden ant, lasius nigerWe eat when we’re hungry, but social insects have to make decisions which will support the colony not just themselves. They typically divide labour as well as reproductive duties. Even in ant species such as Lasius niger where workers are not split into different physical ‘castes’, some workers stay in the nest while others leave to forage. It is often the younger ants who care for the nest while older ants leave to collect food.

Information that individuals could use to decide whether to forage includes their own experience of performing tasks, or their own physiology such as fat reserves. This was investigated in a recent paper published in the Journal for Experimental Biology.

The researchers used an ingenious system where worker ants were tagged with RFID chips which operate an artificial ‘door’ to the nest. Once workers had visited a feeder they were not allowed to leave the nest for a week. A week after the start of the experiment the researchers opened the doors to all the ants. The experiment was to discover whether the ants who had been trapped for longest would be more likely to leave than those who had recently been out.

The answer was yes: those who had been trapped for longest, i.e. the ants who are the leanest, were most likely to leave and forage. They therefore concluded that physiological condition was more important than memory of recent tasks in determining the ants’ behaviour. Such rules about when to forage allow ants to gather food efficiently and flexibly.

Our flying ant survey is looking at another act of ant ‘decision-making’. Do flying ants appear at a specific time determined by the ants’ biology, or is there a lot of flexibility in response to external conditions such as weather? This is an extremely interesting question.

Events in nature such as the emergence of flying ants can be triggered by the time of year as well as environmental conditions. Animals often use changes in day length to determine what time of year it is. But we’re pretty certain that flying ants are also flexible in response to environmental factors. They will almost certainly choose suitable weather conditions to begin their flights. Be on the look out, flying ant day is probably not far away.

Rebecca Nesbit, Press Officer, Society of Biology

Photo courtesy of Roger Key and Buglife.

Elva J. H. Robinson, Ofer Feinerman and, & Nigel R. Franks (2012). Experience, corpulence and decision making in ant foraging Journal of Experimental Biology DOI: 10.1242/jeb.071076

One Response to How does an ant decide what to do?

  1. Margaret Maddison

    Ants about to fly appear to be flexible in response to changing weather conditions. In our garden we have seen on several occasions that when conditions were changing (rain distantly approaching) the flying black garden ants which were leaving the nest turned back and re-entered nest. They appeared to be shepherded to do so by the workers.

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