Locusts in West Africa

Locusts in West Africa

The summer of 2004 was not a good one for farmers in many West African countries. Locusts swarmed over their fields with all the force of a biblical plague, consuming crops and pasture and leaving devastation in their wake. Worst hit were Senegal, Mauritania, Algeria, and Morocco. (See Locusts plague North and Western Africa.) Similar environmental conditions developed over the region between July and August 2008, suggesting the possibility of another locust threat to agriculture.

As summer breeding started in early August 2008, Locust Watch, a unit of the United Nations’ Food and Agriculture Organization, classified the desert locust situation as calm. Relatively few breeding locusts lined the northern Sahel, where the outbreak was concentrated in 2004, but small clusters were gathering in Algeria and Morocco. Clusters of locusts are bad because when many locusts are forced into a small area, they become the aggressive, all-consuming menace long feared by farmers worldwide. In scientific terms, they become gregarious.

It is significant, too, that the clusters are developing in northern breeding sites. These breeding areas are the launching spot for the plagues that sweep across the Sahel. In late summer, clusters of locusts from Algeria and Morocco migrate south where the rainy season sustains seasonal vegetation. In 2008, the rains were intense, and vegetation responded in kind. The deep green that dominates this vegetation image shows that plants were growing faster and thicker than average in July 2008. It reveals that conditions were ideal for locust breeding, with plenty of water and an ample food supply.

If these favorable conditions continue, large swarms of locusts could develop as in 2004 just as the agricultural growing season begins to peak. If not controlled, the locusts could swarm and destroy the ripening crops, creating food shortages. Vegetation images such as this one are valuable in that they show the conditions that could lead to a locust outbreak far in advance of the first swarm. This gives local governments time to prepare a defense. This image was made from data collected by France’s SPOT Vegetation satellite in July 2008. Locust locations are from Locust Watch.

Image created by Jesse Allen, using SPOT Vegetation data provided by the United States Department of Agriculture Foreign Agriculture Service and processed by Jennifer Small and Assaf Anyamba, with the Global Inventory Modeling and Mapping Studies (GIMMS) Group at NASA’s Goddard Space Flight Center. Caption by Holli Riebeek and Assaf Anyamba.