Grasshoppers are known to swarm and to become locusts, i.e. a swarming form of grasshoppers. Under certain conditions these species can breed extremely quickly and their population migrates when then grew dense enough. Swarms quickly strip fields and cause great damage to crops.
Scientists have found what makes grasshoppers to swarm and become locusts. They have proven that if you rub the hind leg of a grasshopper for five seconds every minute and this process continues for four hours, a brain transformation will be triggered. It will cause swarming and the grasshopper will become a locust.
According to experts solitary grasshoppers get together when food is scarce or when there is some danger. As they get close to each other, they start rubbing their hind legs which results in swarming. Increased population of locusts and swarms tend to cause severe damages because they eat grass, leaves and cereal crops.