When cannibals attack: the locust story

Author:  Charley Wang

Institution:  University of Toronto
Date:  June 2008

Locust plagues are indeed spectacular, with millions of insects spontaneously lifting into the air and devouring everything around them. Why so many locusts spontaneously choose to migrate has always been a mystery. The Bible tells how God once caused an enormous plague of locusts to descend upon Egypt, destroying everything in their path. More recently, a team of scientists has found another, somewhat less divine, reason for the movement of these insects.

The team, led by Prince University's Iain Couzin and including professors from the University of Oxford and the University of Sydney worked with immature, flightless locusts and computer models to arrive at the answer: Cannibalism.

It has long been known that in times of scarcity, locusts will turn to eating each other. But the effect of this cannibalism on group behaviour has not been studied until now.

The scientists describe the behaviour as follows. Starving locusts will take bites out of their neighbours. The bitten locusts understandably attempt to flee and their panic spreads to surrounding locusts, who will try to put space between themselves and any others approaching from behind. Aggression and panic then explodes through the population, and causes individual locusts to move forward. Combined, these localized movements turn into a mass migration, with devastating consequences.

Studies of locust movement are part of the study of group dynamics in the animal kingdom. Researchers in this field, like Couzin and his colleagues, endeavor to discover the mechanisms behind the phenomenally complex group movement exhibited by animals. Group dynamics aims to discover how, for example, the phenomenally cohesive movement of tens of millions of locusts can arise from interactions between a single locust and its neighbors. And, in the end, understanding how locusts start swarming could help researchers discover how to make them stop swarming.

Written by Charley Wang

Reviewed by David Metcalfe

Published by Pooja Ghatalia