Locusts are a group of grasshoppers which periodically form dense swarms and cause extensive damage to crops. Locusts live in warm countries such as Africa and India. The locust develops by a process called incomplete metamorphosis, i.e. there is no larval or pupal stage. The eggs hatch into nymphs which resemble the adult insect but they have no wings. In order to grow, the nymphs have to shed their 'skins' (cuticles) and expand their bodies before the new cuticle hardens. At each moult, the wings grow a little larger until the final moult reveals the fully formed winged adult which can fly to a new location.
During mating, the male locust mounts the back of the female and passes sperms into her reproductive tract. The sperms are stored in a sperm sac in the female's abdomen and, as the eggs pass down the oviduct during laying, the sperms are released and so fertilize the eggs. The adult female lays her eggs in warm, moist, sandy soils and the eggs hatch into nymphs which at this stage are called 'hoppers'. The hoppers crawl or hop along the ground feeding on natural vegetation by biting off pieces with their jaws.
When the population is low, the locusts do little damage, eating the natural vegetation. If the hoppers become crowded, they start grouping into in large bands of several hundreds or thousands. The bands move forward at about a kilometre a day, eating all the vegetation in their path. When the nymphs in these bands become winged adults they form dense swarms of flying locusts that can travel thousands of miles. If they land on crops, they can destroy them by eating all the leaves. The species of locust which causes the most devastation is the desert locust. Other species, such as the red locust and the migratory locust can be largely kept under control.
Attempts to control the desert locust depend on constant vigilance to see when and where the hoppers are starting to aggregate into bands. With good communications, insecticides can be sent to affected areas and used on the hoppers or swarms. Aerial spraying is often used. Some of these insecticides are toxic to humans and so great care must be taken in their use. New, safer insecticides are constantly being developed.