The Ant Hill Mob

Most of us have, at some time, watched with fascination as a group of ants work together to bring food back to their nest. We have observed how the 'scout' ant heads the search, leaving behind a faint trail of pheromones for its companions to follow, strengthening the trail with their own pheromones. Although the scout moves randomly, somehow the other ants seem to collectively 'know' the shortest path. How is this so? Mathematicians and physicists have been researching this problem.

The consensus view is that ants follow the straightest path by means of a sequence of successive improvements. The random path taken by the scout is made more efficient by the secondary wave of ants. There is evidence from computer simulations that ants that are forced to change direction sharply either perform a U-turn or keep going but lay down less pheromone. If this is the case, it is easy to see that there will be a gradual build-up of pheromone on the straighter tracks for successive waves of ants to follow.

Physicist Richard Feynman's explanation is similar. He believes that ants trying to follow the original path tend to overshoot at corners and wander off randomly until they meet the path again. The overall outcome of this is that sharp bends are eliminated and pheromone accumulates on the straightest course.

Mathematician Alfred Bruckstein of Technion University in Haifa, Israel, set up a particular method of Feynman's concept and proved that as ants follow each other, their paths become straighter and straighter. His theorem is based on consideration of the angles that each ant turns at a given time. As the number of trips grows, the angle tends towards zero, meaning that the path becomes ever more straight.

A similar phenomenon occurs if ants are given the choice of two routes to the same food source: they will gradually tend towards the shorter one. The pheromone trail will become stronger here as these ants are able to make more trips than their counterparts on the other trail, and ultimately all the ants will switch trails. Zoologist Dr Simon Goss finds the collective behaviour of the ants intriguing: 'No ant has compared the two trails, but collectively they've used a very simple rule and they've used positive feedback.'

These elegant explanations of collective behaviour may have implications for other forms of animal behaviour, such as the flocking of birds or movements of shoals of fish. All of these seemingly collective actions may arise simply from the combination of simple rules followed by each individual.

Issue 2: Contents | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9