The Migratory Locust (Locusta migratoria), is the most widespread species of locust. It occurs throughout Africa, Asia, Australia and New Zealand. It was once very common in Europe but has now become rare there. Because of the vast geographic area it occupies, which comprises many different ecological zones, numerous subspecies have been described. However, not all experts agree on the validity of some of these subspecies.
Pigmentation and size of the migratory locust vary according to its state (gregarious or solitary or intermediate form) and its age (larva, mature or immature adult). Gregarious larvae have a yellow to orange covering with black spots. Solitary larvae are green or brown. The gregarious adult is brownish with yellow, the latter colour becoming more intense and extensive on maturation. The solitary adult is brown with varying extent of green color depending on the color of the vegetation. Gregarious adults vary in size between 1.5 to 2.33 inches according to the sex. They are smaller than the solitary adults.
They transform enormously behaviorally and physically under the effect of population density and are thus called polyphenic insects, or locust. There are two main phases: the solitary phase and the gregarious phase. As the density of the population increases the locust transforms progressively from the solitary phase towards the gregarious phase with intermediate phases.
Locusts are highly mobile, and usually fly with the wind at a speed of about 9 to 12.5 mph. Swarms can travel about 3 to as much as 80 miles or more in a day. Locust swarms can vary from less than one square kilometer to several hundred square kilometers with 40 to 80 million locust per square kilometer. An adult locust can consume its own weight (about 2 grams) in fresh food per day. For every million locusts, one ton of food is eaten.
In Africa, the last serious widespread plague of this species occurred from 1928 to 1942. Since then, environmental transformations have made the development of swarms from the migratory locust unlikely. However, the desert locust which is very similar to the African migratory locust remains a major threat. Nevertheless potential outbreaks are constantly monitored as plagues can be devastating. Locust survey and control are primarily the responsibility of the Ministry of Agriculture in locust-affected countries and are operations undertaken by national locust units.
The Food and Agriculture Organization (FAO) of the United Nations provides information on the general locust situation to all interested countries and gives warnings and forecasts to those countries in danger of invasion.