The Menace of Locusts

The desert locust - schistocerca gregaria - is one of the greatest natural threats to agriculture, and hence to human life, in much of Africa and Asia. It can invade nearly 11 million miles, an area that contains roughly 20% of the world's land surface, 10% of the world's population and all or parts of 65 different countries.

Locusts normally live for about four months but they can slow down their body processes and extend their life span to a year if there is a shortage of vegetation or if the climate is cold. Each female locust produces about 200 eggs in her short life. The young locusts have no wings and are known as "hoppers". They live mainly in sandy desert areas. In dry years when vegetation is sparse locusts resemble green grasshoppers. They prefer to hunt about by themselves for food and to stay away from each other. Their desire for solitude disperses them over wide areas, thus helping the species to survive. But when, at rare and irregular intervals, there are heavy rains in the desert, they begin to breed in enormous numbers. Moreover, their manner and appearance change. They crowd together, touching one another's bodies repeatedly and their colour changes from green to black, yellow and red. They become voraciously hungry and set off in enormous swarms in search of food.

The ability of the locusts to change in appearance was first detected in 1921 by Sir Boris Uvaroy, now in charge of the Anti-locust Research Centre in London, and the leading world expert in the behaviour of these insects. His discovery answered one of the oldest questions about locusts: how did they vanish in some years and reappear in others? The answer was that they didn't vanish. They simply had a diabolical way of escaping attention. They change back to the form resembling ordinary grasshoppers and were mistaken for a separate species.

Locusts also have a remarkably keen sense of smell. This guide the migrating swarms to trees, crops and pastures in their search for food. They can fly at about 10 miles per hour but prefer to be carried by winds and can travel 30000 miles within their lifetimes. Since they breed as they go, the distance that a swarm and its progeny can cover becomes enormous. During the great locust plague of 1968 one group arose from the deserts in the far south of the Arabian Peninsula near Aden, pressed north-wards through Yemen and Saudi Arabia and then crossed the Red Sea turning south again to attack the United Arab Republic and the Sudan, thus travelling approximately 2,000 miles in eight months.

Research into locust behaviour is carried out in the London centre which actually breeds 600,000 locusts a year for experimental purposes. But efforts to control and contain the locust swarms are led by the Food and Agricultural Organisation (FAG) with headquarters in Rome and II field stations, all equipped with radio transmitters ranging from Morocco and Mauritania in the West to Persia and Pakistan in the East.

Unfortunately Nature herself cannot offer any serious challenge to the locusts once favourable conditions for breading have occurred and the swarms begin to multiply. The locust's natural enemies such as certain beetles, flies and wasps are neither sufficiently numerous or mobile to reduce the swarms to any extent and although birds regularly attack locusts their effect is only marginal. Man is now attempting to prevent such plagues by a variety of means.

One method is to scatter poisoned bait in the breeding grounds before the locusts begin to fly. Suitable bail is bulky to transport but can be spread by hand without expensive and sophisticated equipment. The chief difficulty is that the areas where breeding occurs are m- mainly uninhabited and themselves cover a very wide area. Another method is by insecticide sprays which are released on the swarms in the air by a fleet of light aircraft. Light oil is mixed with the insecticide to prevent if from evaporating in the sun or being washed away by the rain. One hazard which the pilots face is that the engines of their planes can become clogged with flying locusts which causes them to return to land. Attack from the air has of course proved vastly more effective than spraying from the ground but the real solution is to destroy the locusts before they become air-borne at all and this requires teams of locusts scouts whose job it is to report any signs of swarms forming.

Recently even space research has contributed to the anti-locust campaign. There is a U.S. weather satellite tracking station at Asmara in Ethiopia. The satellite in space transmits the pattern of wind zones to the station on earth and, since locusts tend to ride with prevailing winds, they normally congregate in a zone and scouts can know where to look for swarms.

Nevertheless human intervention has so far only managed to contain a plague, never yet to stop it from occurring. Yet even this resulted in the saving of 15 billion dollars' worth of crops in 1968, the most recent plague year.

The Arabs in the area of the Red Sea tend to take a philosophical view of the problem. "The locusts are there to show us that life is not ours alone", they say. "It is written that when there are no more locusts there will be no more world.”