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Why Do Locusts Swarm?

  • Carol Pearson

In Africa, heavy rains and drought bring swarms of locusts, which can destroy enough food in one day to feed 200 million people.

Now a scientist in Britain believes he has discovered why mild-mannered grasshoppers become migrating swarms of locusts that devour all the plants in their path, from field crops to leaves on trees.

When rains are heavy and vegetation thrives, locusts feast, and their numbers explode. In places like Africa, the consequences are catastrophic. A swarm of locusts can eat about 80 thousand tons of vegetation a day. But why do locusts swarm? At Britain's Oxford University, Dr. Steve Simpson has been studying locust for the past 25 years.

"You can see that at the heart of the locust problem is the fact that these animals (insects) can change from a non-swarming to a swarming form. And if you can understand that process, then you can see the potential for developing new ways of predicting and controlling the animal (insect)," says Dr. Simpson.

But, again, why do locusts swarm?

Dr. Steve Simpson says, "The reason they change is because of crowding."

When heavy rains are followed by a drought, locusts are forced to crowd around dwindling food sources. Dr. Simpson's team is trying to figure out how crowding leads to swarming. They discovered that sight, smell and sound seem to play no role. Then they looked at touch.

"So we divided the body surface of the animal (insect) up and then we tickled one of those particular body regions with a paint brush. And we tickled one of these body regions with a paint brush for five seconds, each minute, for four hours. And at the end of that, it was found that the only place which caused them to change into the swarming form was being touched on the back leg," says Dr. Simpson.

When locusts crowd together, they accidentally rub these hot spots. And that tells them to swarm. If researchers can stop the trigger, they can stop the swarm. And if they can stop the swarm, they can save countless lives in Africa.

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