Normally, the desert locusts mentioned in the Bible are shy and reclusive and are green in color. What turns them into the multi-colored army that sweeps across the land, eating every leaf in sight?
Even the book of Proverbs marvels at how locusts, without any leaders, behave like a destructive army. Yet they live most or all of their lives as grasshoppers. However, there are seven species of these locusts that now and again can become a destructive swarm. It happens when their population spikes, usually due to an abundance of food. But what triggers the change? Researchers put a rolling ball around in a cage to jostle a solitary locust. After a few hours the locust was ready to jostle fellow locusts. Then researchers next took a small paintbrush and began to tickle various parts of the insect. After long, tedious hours of locust tickling they found that simply touching a locust's hind leg made it ready to swarm. They concluded that when the locust population spikes, the insects begin to jostle each other, and that touching turns them into a destructive swarm.
One might conclude that when God wanted to punish people in Old Testament times with a plague of locusts, He simply blessed the locusts until they began to jostle against one another. Then they were ready to swarm at His bidding.