Your average locust is actually solitary beast who will actually shun other locusts. So the question is, why does a solitary animal suddenly turn gregarious with such a vengeance that it turns into a super organism that causes huge devastation?
A recent Catalyst program looked at the work done on this by a joint Cambridge and Sydney team. It appears that if the hairs on the back legs are stimulated (through contact with other locust - or a paint brush in this instance) for several hours, the locust turns from a loner to gregarious.
This short time frame meant that the cause of the the change had to be chemical, and not through a re-wiring of the nervous system.
When they studied gregarious locust they found that they has elevated levels of serotonin.
Serotonin is found in the human brain, and low levels are associated with depression. Prozac works by increasing serotonin levels. High levels of serotonin are associated with happiness. This is how Ecstasy works.
But there's something else going on. The swarming doesn't happen until there is a critical mass of locust. Then they all start moving in the same direction.
So strong is the urge to move together, that any that do not are set upon and eaten by the others.
So it looks like locusts invented the rave party long before humans.
Now that the chemical that triggers the gregarious behaviour has been found, a solution presents itself.
The only trouble is, how do you persuade several million drugged-out locusts to drink a glass of warm milk and have a good lie down?
Michael L. Anstey, Stephen M. Rogers, Swidbert R. Ott, Malcolm Burrows, and Stephen J. Simpson. . Science 30 January 2009 323: 627-630 [DOI: 10.1126/science.1165939]