Certain kinds of locusts such as the Red Nomadacris spp and the African Migratory species, a variant of Locusta migratoria, have reasonably well-defined outbreak areas. They can often be detected and suppressed before they reach plague proportions. But Schistocerca spp is the exception. It is nomadic. It can emerge in countless millions from the breeding and concentration of insects widely scattered, in altitudes from sea level to 10,000 feet, as well as from swarms that survive a recession period. A major swarm of these metallic black-and-yellow locusts can shadow an area of 500 square kilometres or more, in layers up to a kilometre deep. There will be ten thousand million insects in such a swarm, a flying mass of 50,000 or 100,000 tonnes. A swarm can fly 3,000 miles overland, normally in 10-hour daily flights at air-speeds of only a few miles an hour. The locusts hold reserves of fat adequate even for overseas flights (wind-tunnel tests indicate flight times of up to 17 hours).
Locusts and grasshoppers are any of the leaping insects of the family Acrididae, which at times multiply greatly and migrate long distances in destructive swarms. In Europe the term 'locust' connotes large size; smaller acridids are called grasshoppers. In North America 'locust' and 'grasshopper' are used for any acridid. They are almost entirely herbivorous, and among them are some serious crop pests. They constitute the most abundant and widely distributed pests in the insect order Orthoptera. Some species are restricted in their feeding habits to certain plants, but most feed on any suitable vegetation. Natural controls (mainly predators, birds, frogs, snakes and the larvae of certain flies) check the populations of most species, and they usually occur in insufficient numbers to cause serious damage. A small number of species known as locusts, experience massive population explosions and because of their strong migratory habits, they cause widespread and terrible destruction. A number of other species, without reaching such devastating proportions, are still highly destructive of crops and rangelands especially in North and South America, Africa and Asia.
Grasshoppers are virtually cosmopolitan, being found in a variety of habitats - mountains, deserts, temperate forests and grasslands - but they occur in greatest numbers in lowland tropical forests, semiarid regions, and grasslands. The outbreak areas of the migratory locust of the old world Locust migratoria, are of four ecological types: (a) deltas of rivers entering the Caspian and Aral seas and Lake Balkhash (and similar situations in China and Africa), surrounded by arid sand tracts; there the extent of the grassland habitat of the locust changes greatly as a result of irregularities of floods; (b) grassland areas adjoining deserts, subject to extreme fluctuations in precipitation with corresponding changes in extent of habitable area; (c) islands of dry warm soil in the central USSR, a region generally too cold and wet for the species; there overcrowding occurs after several exceptionally warm dry years; (d) grasslands produced by periodic burning in the unfavourable, humid forestlands of the Philippines; their extent varies greatly, leading to overcrowding and production of the gregarious phase.
The outbreak of locust swarms presents a serious threat to agriculture and therefore to the well-being of millions persons dependent on the crops for their food and livelihood.