Behavioural study could put an end to the eighth plague

By drawing a parallel of locusts to the behaviour of physical systems, the researchers have shown that the complex dynamics of moving animal groups can be captured by a very simple mathematical model

A study of locust behaviour will help scientists predict the onset of collective motion in insect swarms, leading to improved control measures for these hugely destructive events.

The study, published in this month's Science magazine, was undertaken by an international team of researchers including Dr Jerome Buhl and Professor Stephen Simpson from Sydney University's School of Biological Sciences. They focussed on the behaviour desert locust (Schistocerca gregaria), which forms large flying swarms that can devastate crops and affect the livelihood of people across sub-Saharan Africa and Asia.

'Better understanding the process by which they form is the key to the control of these swarms, in which large bands of wingless juvenile locusts (hoppers) come together and begin to march in the same direction,' said Professor Simpson.

'We performed a laboratory study of groups of locust hoppers at different densities. We showed that at a critical density these groups spontaneously adopt a common direction. This transition to order motion could explain the often sudden emergence of hopper bands in Africa,' he said.

The study is one of the first examples in animal biology of a group dramatically changing its behaviour as it reaches a critical mass. By drawing a parallel of locusts to the behaviour of physical systems, the researchers have shown that the complex dynamics of moving animal groups can be captured by a very simple mathematical model. The model, which was based on the alignment of 'self-propelled particles' (SPPs), predicted unstable switching of group direction.

'We observed such switching in the laboratory and this could explain the highly unpredictable collective motion of locusts in the field. Since SPP models underlie many theoretical predictions about how groups form complex patterns, avoid predators, forage, and make decisions, these results have fundamental implications for how we understand all aspects of the motion of animal groups,' said Professor Simpson.

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