The migratory locust (Locusta migratoria) is the most widespread locust species, and the only species in the genus Locusta. It occurs throughout Africa, Asia, Europe, Australia and New Zealand. While once common in Europe it 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. Many other species of Orthoptera with gregarious and migratory behavior also go by the name 'locusts'. Locusta migratoria is a polyphenic species, that is, its pigmentation and size vary according to its "phase" (gregarious or solitary form) and its age. When population densities grow high the migratory locust appears in its smaller gregarious form, which is yellow to orange with black spots. In contrast, solitary form adults are brown or green, and tend to match the vegetation around them. Locusta migratoria in large population numbers can be economically devastating, as both larvae and adults eat huge quantities (adults daily eat their weight in food), and adults, as strong fliers, are highly mobile. Populations are monitored carefully to avoid and control plagues.

Wikipedia 2011a; Wikipedia 2011b