Although locusts are a type of grasshopper, they differ physiologically and in their behaviour. When environmental conditions allow, locusts multiply rapidly so that billions of them can aggregate and migrate vast distances devouring every growing green thing in their path. Plagues of locusts have occured for a long time and are even referenced in the Old Testament of the Bible. The magnitude of damage and crop loss that they can cause is enormous and beyond imagination. They have been the cause of starvation across continents in the past. The desert locust, Schistocerca gregaria (Forskål) is the most widespread and destructive of all locust species. When they invade they can cover about 30 million square kilometres and can include all or parts of 64 countries in the northwest and east of Africa, the Arabian Peninsula and central Asia, including Afghanistan, India, the Islamic Republic of Iran and Pakistan, among others.