In-depth: The Eighth Plague - West Africa's Locust Invasion

WEST AFRICA: A hundred million dollars to fight an age-old plague - The phenomenon of locust infestations

Locust larvae
NAIROBI, 1 December 2004 (IRIN) - Known references to locusts date back to ancient times. They are to be found in the Holy Bible, which describes an insect plague that afflicted Egypt, and in the Holy Qu'ran (7 Al-Araf, 133).

In the Bible, Exodus 10 describes the plague as follows: "The locusts - covered the surface of the whole land, so that the land was black; and they ate all the plants in the land and all the fruit of the trees - nothing green was left."

This is precisely what happened this year in parts of West Africa, devastated by insects which alone, are inoffensive enough, but become a natural disaster of continental proportions - sometimes affecting more than one continent - when they swarm.

From the individual to the swarm

Photo: FAO
A carpet of locust larvae
The desert locust belongs to the family of crickets, known as the Acrididae. Where humans are concerned this member of the cricket family is the most destructive. It becomes gregarious when it joins others in a high-density swarm. This social development - gregarious locusts are especially voracious - during the life of the locusts goes hand in hand with a morphological transformation. The initially solitary locust doubles in size, making it capable of devouring its own weight - 2 grams on average - each day.

The locust goes through three successive growth phases. It begins its life in the egg, where it stays for ten to 65 days depending on the climate, before emerging as a larva. It remains at that phase for an average of 36 days, then develops wings and lives for another two and a half to five months. Few locusts live more than 6 months, but in that time their mobility and consumption patterns can have severe consequences on human society.

The black larvae grow into salmon-coloured youngsters measuring about 10 centimetres, a little longer than the average cigarette. Fully mature adults are lemon yellow in colour. The adults can reproduce twice or thrice during their lifespan. Each female lays between 90 to 140 eggs at a sitting. With proper climate conditions, an average female can produce between 400-500 offspring. These reproductive statistics explain the extraordinary, exponential growth of locust swarms in a short period of time.

Photo: DURANTON J.-F. & LECOQ M., 1990
The locust's habitat
The billions of insects that form a swarm behave as a perfectly coherent group, moving together in one direction.

A vicious circle

Climate conditions need to be conducive for the swarms to thrive. How well the locust multiplies paradoxically depends on the same climatic factors that favour the farmers and make for good harvests. Good rains are this factor. Similar conditions facilitate the high and successful birth rates of the insects. Sandy soils, or humid clay-like soils, are also an ideal environment for laying.

Abundant green vegetation is essential to the locusts' development into mature insects. Crops provide the food the locusts need to reproduce massively. It is a cruel irony that weather conditions ideal for farmers also provide the basis for the destruction of their fields.

Photo: IRIN
Adult locusts mating in September 2004
The locust's usual habitat stretches from West Africa to India and from Spain to Tanzania. In most of these countries, the population depends mainly on agriculture. However, the first swarms are often hatched in the Sahel, the huge band of arid land just south of the Sahara, from Senegal to Egypt.

Up to October 2004, the current crisis affected 10 West and North African countries - Algeria, Burkina Faso, Cape Verde, Chad, Mali, Morocco, Mauritania, Niger, Senegal and Western Sahara. Since then, it has spread to the Middle East. One of the most remarkable characteristics of the locusts is their mobility. They can travel an astonishing 200 kilometres (km) a day by surfing on winds at an altitude of 1,500 metres.

During the last major locust invasion in West Africa, many swarms crossed the Atlantic Ocean in 1988, reaching the Caribbean and South America in 10 days of uninterrupted flight. However, the 1988 crisis was much smaller in scope than this year's, according to Said Ghaout, director of the national anti-locust centre in Morocco.

Photo: FAO
Young locust
While seasonal migrations of locusts depend on the winds, the insects generally travel southward from Northwest Africa to the Sahel in early summer. In autumn, they head back to North Africa.

Devastating habits

The swarms stay on the ground at night, perched on the plants they devour. From dawn, they bask in the heat of the sun for hours before taking off. This is the ideal time to spray them with pesticides.

It is not rare for a swarm to measure 20 km long and 5 km wide, i.e. the equivalent of 10,000 hectares (ha). At an average density of 500,000 individuals per ha, such a swarm would comprise five trillion individuals and eat 10,000 tonnes of vegetation per day.

The locusts' invasion of Mauritania in the summer of 2004 caused a dire shortage of mint, which is of central importance in the preparation of the local tea.

Nothing green escapes their voracity. The locusts devoured the lawn of the football stadium in Nouakchott, the Mauritanian capital, during the quarterfinal match of the President of the Republic Cup, in October 2004.

A season in hell

Photo: IRIN
The most voracious and harmful stage of the locusts' development is when they are pink and winged
In 2004, the locusts invaded the Sahel at a time when farmers were particularly vulnerable, in the lean season just ahead of the harvests. Food stocks had been exhausted and all the money made from previous harvests has been re-invested in seeds, which should soon have borne fruit.

Mame Dieng, a village chief in Rao district in northern Senegal, lost everything in early October.

"We were three weeks away from the harvests and people had sunk all their savings into the seeds they planted," he told IRIN, pointing wearily to a succession of short stumps stretching over hectares that used to be peanut fields.

Dieng said the inhabitants of certain villages in the region had begun to migrate to the big towns to look for work, driven by the need to maintain their livelihoods. Many of those who remained behind will have to sacrifice their children's education, since they have no money to pay for it.

"Every year it's something, not enough rain, grasshoppers [equally harmful to crops] and this year the locusts," he sighed.

Photo: IRIN
Locusts eating their dead
The exact consequences of the crisis for food security in West Africa were still uncertain in October, but assessment missions found entire departments devastated by the insects in Senegal. In Mauritania, the worst affected country of the region, the UN Food and Agriculture Organisation (FAO) estimates that up to 50 percent of the food production has been lost to locusts.

According to the FAO, US $100 million is needed during the autumn of 2004 to prevent the plague from recurring next year. However, by the end of October, the FAO had raised only half this amount.

Ironically, locusts do not depend on good harvests as much as humans to be able to survive. In lean times, they devour their dead, thus enabling the bulk of the swarm to continue its destructive course. If the current generations survive to winter in North Africa, they will give birth to a new one and the cycle of devastation will continue in spring 2005.