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Volume 18, Number 6November/December 1967

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Plague Across The Land

Written by Daniel Da Cruz
Photographs courtesy of Food and Agriculture Organization of the United Nations
Additional photographs by Ahmad Mentakh

"...And they shall cover the face of the earth, that one cannot be able to see the earth, and they shall eat the residue of that which is escaped... and shall eat every tree which grow-eth for you out of the field. And they shall fill thy houses."

No one who has ever seen the locust at work accuses the Biblical account of hyperbole. In 1926-27, small swarms of the African Migratory Locust were spotted in an area 50 by 120 miles on the plains of the River Niger near Timbuktu. The next year swarms invaded Senegal and Sierra Leone. By 1930 the whole of West Africa was flailing away at the pest with everything movable. But the locusts didn't seem to notice; swarms reached Khartoum, more than 2,000 miles to the east of Timbuktu, then turned south, spreading across Ethiopia, Kenya, the Belgian Congo, and, in 1932, striking into the lush farmland of Angola and Rhodesia. Before the plague finally sputtered out 14 years after it began, it affected five million square miles of Africa, an area nearly double the size of the United States.

The locust is perhaps nature's most awesome example of the collective destructive power of a species which, individually, is practically harmless. An adult locust weighs a maximum of two grams—it takes over 225 to outweigh a can of beans. But since each locust can eat its own weight daily, and since a moving swarm may carpet the ground with anywhere from 30 to 60 locusts a square yard, a square mile will typically contain from 100 million to 200 million of the creatures. Seldom, furthermore, will a swarm occupy a mere square mile; swarms more than 400 square miles in area have been recorded, and one that size weighs more than 80,000 tons. It numbers around 40 billion insects eating the weight of the Queen Mary every day it is on the move—and it never stops. Even the two tons of locusts each one million population represents takes a tremendous toll: each day that population eats as much as 20 elephants or 500 people. And their voracity is not only in numbers; pound for pound the locust eats 60 to 100 times as much as a human being.

The ubiquity of the locust makes eradication of the pest about as easy as emptying the Atlantic with a teaspoon. Destructive grasshoppers and locusts infest most of Africa, central and western North America, about half of South America, the Arab world, Australia, the Indian subcontinent, and a broad band across Central Asia. One of the three main species, the Desert Locust, may invade 11 million square miles, more than 20 per cent of the world's land area. The African Migratory Locust is so far confined to Africa below the Sahara. The Red Locust, third of the terrible triumvirate, breeds unobtrusively in a section of Mali and Niger, then breaks out in swarming billions into an area 400 times the size of its breeding grounds.

For all their economic importance in large areas of the world, there is considerable confusion about what a locust is. In the United States, the name is frequently used interchangeably for grasshopper, locust, and the cicada. The cicada is not properly a locust at all, but the locust's relation to the grasshopper as real, in that they both belong to the superfamily Acridoidea. Locusts may be defined as grasshoppers which have the capacity to change their habits and appearance when they congregate in dense groups. These groups are called sands when composed of young wingless locusts, and swarms when of adults that fly. In the Arab world, the two most important species are the Desert Locust (Schistocerca gregaria) and the African Migratory Locust (Locusta migratoria nigratoria). A further distinction—a frustrating one that keeps locust control officers on the hop—is that unlike all other species, the Desert Locust has no permanent outbreak area, and can spring from practically any soil.

The locust passes successively through the stages of egg, hopper and adult, with maturation occurring between two to four weeks under optimum conditions of temperature and humidity, and as long as six months during periods of drought and low temperature. A female lays her eggs in soil damp enough for her to thrust her ovipositor two inches straight down into the earth, where she deposits a cylindrical cluster, or pod, of eggs in bout two hours. A female can lay nearly 300 eggs in two or three pods, and where warms come to earth to lay their eggs, the field may extend many square miles. The incubation period between laying and hatching is quite variable: between 10 and 14 days during summer breeding in Ethiopia, to 25 and 30 days spring breeding in the Arabian Peninsula, to 50 and 70 days winter breeding in Iran ir northern Syria and Iraq in very cold weather.

Young hoppers burst from their shells around sunrise and at once shed a thin white skin. The next day they begin to feed, and, as they grow, to shed at intervals the tough carapace that estricts each phase of their growth. One growth stage succeeds another until the inal moult when the hopper becomes a ledgling adult. Its length stabilizes at from two to three inches, but to achieve its adult weight of two grams the hopper has already eaten 10 times that weight—and it is only getting warmed up, for as an adult it can fly to get its food while as a nymph it could only hop. Flying or hopping, the locust will have but brief glory: its life span typically covers 14 days as an egg, 38 days as a hopper and 75 days as an adult, still time enough to consume 170 times its weight.

When hoppers occur in large numbers as a result of favorable weather conditions in localities of swarm breeding, they form bands which move as a unit. Bands of the Desert Locust, for instance, spend the day marching in a definite direction—usually downwind—feeding as they go. When the temperature is above 97° F., around midday the band roosts off the ground on rocks or bushes, and if the weather is very hot the locusts' siesta may last as long as four hours. Thoroughly rested, the hoppers resume their march until nightfall, when they seek foliated perches above ground for their heavy meal of the day, and sleep on the denuded remains of their feast. Unlike an army, whose progress slows as it grows, the bigger the band the faster it moves. Some bands can transform green fields to brown stubble at the rate of one linear mile a day.

Compared with the adult, though, the hopper is a slow-moving country cousin. Locusts on the wing are marvels of stamina. Indeed, locusts hold the flight endurance record for insects by a wide margin. Wind tunnel tests show that they can flap their wings non-stop for 17 hours, and in nature they may be able to fly at a cruising airspeed of 10 to 12 miles per hour for 20 hours or more. Gliding on thermals like sailplanes, they can stay in the air even longer and thus make incredibly long journeys, such as the confirmed 1954 flight of a swarm from the Canary Islands to the British Isles, a distance of 1,600 miles. Old sea stories have it that in such flights some locusts land in the water to make a platform on which the others rest and from which they take off, but confirmatory evidence is lacking. Like planes, they take off and land into the wind (and in high wind take shelter), aided by a low weight-to-body-area ratio and wing-root muscles which at normal working speed outperform 10 to 20 times human muscles working at top speed.

When the hoppers emerge as winged adults, the bands become swarms with vastly increased mobility, and an average density of around 130 million per square mile. Adulthood brings a change in living patterns, too. The Desert Locust, for example, roosts from an hour after sunset until sunrise, and for the first half hour of the day is a slugabed, up but not around. Two hours of aimless milling and short flights apparently starts their blood circulating, and at about nine o'clock they take off on the rising convection currents boiling off the desert. Until sunset the swarm is continually airborne, with locusts on the leading edge coming down to rest and feed while the main body of the swarm passes on overhead, after which they rise again into the air at the trailing edge of the swarm, creating the effect of a giant millstone grinding its way across country.

Depending on wind conditions, collective movement ranges from a few miles to more than 60 miles daily. As swarms fly mostly downwind, weather maps showing wind currents help locust control missions predict the areas where swarms are most likely to converge, and thus where their efforts at extermination of the insect will be best repaid. When they fail, trying times are ahead for any living thing lying in the swarm's path. Long-time Kuwait resident Col. H. R. P. Dickson told of an invasion of the Red Locust which advanced on a five-mile front so dense that even metal screens failed to keep them out of houses. For days, the locusts ate everything in sight. They chewed through carpets and upholstery, Colonel Dickson reported. Even dishes at dinner "were served with dead dibbas disconcertingly floating about the gravy or imbedded in the rice." Several thousand sheep, deprived of fodder, died of starvation, but wild animals, camels and dogs waxed fat on a nourishing diet of Red Locusts.

Locusts of the same species are so differentiated in response to environment that until Sir Boris Uvarov disproved it, in 1921, they were considered distinct species. Desert Locusts in one phase, for instance, are relatively long-lived, lay over 90 eggs per pod, develop slowly, never form groups or march in concerted fashion, move no more than a few yards daily, and often fly at night. The same species in another phase usually lay 80 eggs per pod, are short-lived, develop quickly, form dense groups that march in concert, move up to a mile a day, and fly mainly by day in the adult stage.

Appearances are similarly misleading. Locusta migratoria migratoria solitarious hoppers are green while their gregarious phase are orange and black. Organs vary in size and shape between the two phases, and using indices computed from differential measurements which show that changes from one phase to another are beginning is one of the principal methods by which scientists are alerted to the imminency of a plague. Other than by this means, locust control authorities are practically powerless to predict where they will appear. How long a plague will last and the amount of destruction it will wreak are similarly mysteries, although the amount and distribution of rainfall and weather in general are fairly well implicated in the overall pattern of locust plagues.

Fortunately for mankind, plagues die out sooner or later even when food is plentiful, but the explanation for the disappearance of the swarms is as obscure as the mechanism which starts them in the first place. Though morphologically locusts have extreme phases, the changes follow a circular pattern, from solitarious through a congregating phase into gregarious, then through a segregating phase back again to the solitarious. Just what triggers each change is something any biologist would give up a sabbatical counting grass skirts in Tahiti to discover.

Meanwhile evidence is piling up, much of it statistical, which provides valuable clues to the dynamics of locust behavior. Two thousand records of locust invasions show that 8 percent of the damage is done by hoppers, 69 per cent by fledgling and maturing swarms, and 23 per cent by mature swarms. Sixty-six pounds of pasturage per acre may be lost in a single day—catastrophic in areas of thin cover like the Middle East—and when the locusts mount trees to graze and rest, their combined weight often brings the defoliated tree crashing to the ground. Records also show that plagues are more common than the layman appreciates: over a 25-year period, Desert Locust swarms were reported from 18 to 23 times annually around the southern rim of the Arabian Peninsula—as high an average as found anywhere in North Africa and Southwest Asia where this locust occurs, and hopper infestations were reported an average of 12 to 19 times a year for the same area.

Mankind no longer mutely accepts its fate, but fights back with a whole arsenal of weapons. The metaphor is apt, because in most respects human warfare has a precise analog in locust control. Intelligence is the first requirement for reporting of conditions which are favorable for the development of the swarms. The second requirement is an efficient transport system, coordinated by a tight-knit organization capable of crossing national boundaries at will. The third is a wide spectrum of poisons, each tailored to specific conditions. The factors of cost, transport, and killing power versus safety must all be considered in selecting the biological warfare agent. DDT, for example, is cheap but doesn't bother locusts particularly. Dieldrin is potent, but toxic to animals and man. Aldrin is cheap and less toxic than dieldrin, but less persistent. Diazinon kills the adult Desert Locust efficiently but little affects hoppers; on the other hand, it is not very toxic. The Parathion family is the cheapest and most deadly of "locusticides" known, but it is hazardous to mammals. Ultimately, the battle against the locust is fought on terms familiar to defense departments everywhere: kill the largest concentrations first, by the cheapest method possible, so as to get the most killed for the least money.

A further decision is whether to fight on the ground or in the air. Meal or bran mixed with poison is effective, but it takes considerable time and truck transport, both disadvantages in remote areas. Dusting requires that the dust falls on the food or the locusts themselves; wind or air turbulence can thwart dusting, but it is cheaper and faster than baiting. Air spraying covers large areas quickly, and even flying swarms (which can be seen up to 60 miles away by aerial spotters) can be effectively attacked by releasing a curtain of spray through which the downwind-flying swarm must pass. A typical attack on a flying swarm might call for a flight altitude from 300 to 500 feet above ground over the densest part of the swarm, starting at one hour before sunset, on a course 90° to the prevailing wind, spreading 16 gallons per minute of 15 per cent gamma-BHC in oil.

The Eastern Province of Saudi Arabia has long been a battleground in frequent assaults against the Desert Locust, since the area was a springboard for airborne invasions of the Indian subcontinent. Indian mission launched major control efforts in the spring of 1958 and again in 1961 and 1962 when eruptions of the locust threatened to spill across the Indian Ocean. With logistic support from Aramco's Aviation Department, a 21-man locust control team fielded a task force from al-Khobar into the rural regions where locust eggs were reportedly hatching. Eight trucks, six power dusters, two power sprayers and 100 hand dusters distributed 50 tons of BHC as dust, spray, and as food bait in the path of the hoppers. The campaign was not entirely successful, for farms around Hofuf were hard hit, the locusts stripping vegetable plots and even attacking the usually untouched leaves of tall palms. Unquestionably, however, the Indian anti-locust teams dulled the aerial spearhead aimed at their homeland by tackling the menace before its momentum became irresistible.

In any case, the locusts do not always have things their own way. Frost decimates their ranks, and high, dry heat will kill them off when shelter isn't available. Too much rain will rot their egg pods or wash them away, and young hoppers can drown in the flash floods that occasionally rip through desert wadis. Wasps and flies destroy many eggs, sometimes eating them or planting their own larvae on them as a future off-the-shelf food supply. Locusts are also cannibalistic, especially in conditions of low humidity. Ants, birds, and other predators from foxes to snakes eat locusts, but despite their voracity make a very small dent in the swarms. Bustard have been shot down with up to 130 hoppers in their stomachs, kite with as many as 168, and European storks with nearly 1,500. The all-time locust-eating record belongs to the Abdim stork, one of which was killed with the remains of 3,481 locusts inside. This suggests a simple solution, but for one complication: what happens to the already soaring human population with so many storks flying around?

Daniel da Cruz, who makes his home in Beirut, is a novelist and Middle East correspondent for a large news agency.

This article appeared on pages 20-25 of the November/December 1967 print edition of Saudi Aramco World.


Check the Public Affairs Digital Image Archive for November/December 1967 images.