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  • 17 November 2005

How ants know the way to "home, sweet home"

Sweet memories: Fed (left) and unfed wood ants

Sweet memories: Fed (left) and unfed wood ants

Ants have long been regarded as among the intelligentsia of the insect world for their organisational skills and efficiency. Now scientists are beginning to understand more about the role of memory in their behaviour.

Researchers at the University of Sussex have discovered that wood ants (Formica rufa ) are able to retrieve the correct visual memory to enable them to either find their way back home, or to reach a food source.

Neurobiologists Dr Rob Harris, Dr Natalie Hempel de Ibarra, Dr Paul Graham and Professor Tom Collett trained individual ants to follow a short foraging route parallel a black wall. The wood ants, which naturally rely on visual cues, learned that the wall would be on their left when walking towards the food, but on their right when walking home.

In later tests, trained ants were deposited midway along the wall. Unfed ants remembered that, in order to reach food, they had to walk in the direction that placed the wall on their left, whereas previously fed ants walked in the opposite direction.

Professor Collett says: "Some ants are known to have surprisingly large memories. For instance, they will remember enough visual landmarks to follow visually guided routes over tens of metres between their nest and a feeding site. One problem with having many memories is that one must be able to retrieve the right memory in the right situation."

He points out that the world looks different when viewed in the two directions, so that the ant has to keep its memories of how to reach food separate from its homeward memories. Otherwise it might become very confused partway along the route.

"We were interested in seeing whether the ant's motivational state - hungry or sated - might trigger which visual route memories it retrieves," says Professor Collett. "We found that in exactly the same visual environment, wood ants retrieved memories appropriate to their food-ward journey when hungry and to their homeward journey when full."

This is not the first cue that has been found to prime insect memories. It's long been known that ants and bees, will retrieve different navigational memories at different times of day. They know which feeding site will have food and take the route appropriate to a particular time of day, ignoring the other routes that they also know.

Notes for editors

Press Office contacts: Jacqui Bealing or Maggie Clune, Tel: 01273 678888, email:

Priming of visual route memories', a research paper, by Dr Rob Harris, Dr Natalie Hempel de Ibarra, Dr Paul Graham and and Professor Thomas Collett, is published in Nature, 17, November, 2005.


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