Why are locust swarms spreading so fast?

A devastating outbreak of locusts is spreading across parts of Africa, threatening millions of people with hunger. The insects are travelling in huge swarms that can be as big as some major cities, sometimes about 1.5 times the size of New York City. Officials say the number of overall locusts could grow up to 500 times by June, when drier weather begins. These are worrying prospects. The National's Suhail Rather delves into the issue to explore why the swarms are spreading so fast and so wide.