ONE of the problems about locusts is the unpredictability of their behaviour. If all goes according to plan, however, a team of biologists and mathematicians from the University of Sydney will soon descend on a swarm and try to resolve the mystery.

Before locusts fly, they march. Millions of juveniles crawl up to 500 metres a day, munching everything in front of them, in bands that stretch for kilometres. This is when the Australian Plague Locust Commission (APLC) tries to reduce their numbers, by laying strips of insecticide in their path. But often a swarm changes direction without warning.

The university group, led by Jerome Buhl, suggests that such changes of movement are mathematically similar to the behaviour of a magnetic material like iron—which, if heated above a certain temperature, known as the Curie temperature, loses its magnetism. In both of these examples interactions between individual particles (magnetic domains in the case of iron, individual insects in the case of locusts) drive sudden changes in group dynamics. The iron stops being magnetic. The locusts change direction.

The next couple of months should be a good time to investigate this theory. Widespread heavy rainfall in inland areas during the Australian summer and autumn produced favourable habitat conditions for females to lay several batches of eggs. This means the nymphs will have plenty to eat when they hatch. Chris Adriaansen, the APLC's director, therefore expects Australia to face its worst locust plague for decades during this springtime.

This unfortunate state of affairs will give two of Dr Buhl's colleagues, Stephen Simpson and Gregory Sword, plenty of opportunity to observe the behaviour of the locusts. When a swarm is detected, the scientists will scoop up a few dozen insects and glue little reflectors on their backs. The swarm will then be monitored by pilotless drones that flash a light at it every five seconds and record reflections using an on-board camera. That will allow individual insects to be tracked, in order to see if they behave as Dr Buhl predicts.

If they do, the next question is: what phenomenon stands in for heat in the case of locusts, pushing them to the entomological equivalent of the Curie temperature? One possibility is the tendency of young locusts to eat one another. This is believed to be why they march in crowds. By keeping on the move they avoid becoming a meal for a neighbour—surely a powerful incentive for a sudden change of direction, too.