16 December 2004

Computer Modelling of Ants

In a collaboration between the Departments of Computer Science and Animal and Plant Sciences, we have discovered that Pharaoh ants use angles to determine the direction of a trail, informing them whether they´re travelling to or from the nest. The study, published in Nature on 16 December, explains how ants know which direction they are travelling in when following pheromone trails.

Duncan Jackson, from the Department of Computer Science at the University of Sheffield, and lead author of the study, explains, "Some ants find their way by following pheromone trails, rather than by using sight. The ants should move away from the nest when they are foraging, and back towards it when they are laden with food but the pheromone trail leaves no way of knowing in which direction the ants are travelling.

"We found that it isn´t the pheromones themselves that determine direction but the angles that they are laid in. The trails are laid at 60 degree angles across the whole network. This means that the ants can tell which way they are going along any trail in the network."

Prof. Mike Holcombe of the Computer Science Department at the University of Sheffield explains, "This was a genuine collaboration between Computer Science and Biology. We in Computer Science have expertise in modelling complex systems including biological ones and the approach we took was strongly influenced by this - in fact the project is a good example of what is being called 'Systems Biology' - a rapidly growing and highly fashionable area. By looking at the whole system, in this case the ant community, we try to understand how all the parts fit together into a working system."

Francis Ratnieks, from the Department of Animal and Plant Sciences also at the University of Sheffield, and co-author of the study explained, "There have been many theories about how ants follow trails, including one by Richard Feynman, a well known physicist.

"He proposed that the ants left three different pheromones, one after the other, so that the ants could distinguish direction by the order of the pheromones in the trail. This solution is extremely complex with thousands of ants leaving pheromone the trails would become blurred eventually resembling a piece of paper with three words written on top of each other thousands of times.

The actual mechanism is remarkably simple and demonstrates that sometimes the best solutions are the simplest."

For further details see : "Trail geometry gives polarity to ant foraging networks ", Duncan E. Jackson, Mike Holcombe, Francis L. W. Ratnieks, Nature 432, 907 - 909 (16 Dec 2004)