The desert locust, Schistocerca gregaria, is a species of short-horned grasshopper that inhabits the arid and semi-arid regions of Africa, the Middle East, and Southwest Asia. Under specific environmental conditions, these insects undergo a dramatic transformation, forming immense, mobile swarms that can devastate agricultural landscapes. This ability to shift from a harmless solitary insect to a member of a destructive collective makes the desert locust a significant threat to food security and economies.
The Two Phases of a Desert Locust
The desert locust exhibits a phenomenon known as phase polyphenism, allowing it to exist in two distinct forms: solitary and gregarious. In its solitary phase, the locust is inconspicuous and harmless. Its coloration, typically greenish or brownish, provides camouflage by matching the surrounding vegetation, and these individuals live isolated lives.
A dramatic shift occurs when locust populations increase, leading to crowded conditions. The trigger for the transformation to the gregarious phase is physical contact among the locusts, specifically the repeated touching of their hind legs. This stimulation prompts a surge in serotonin, a neurotransmitter that alters behavior and appearance, causing locusts to attract one another rather than repel.
Nymphs, known as hoppers, develop bold yellow and black coloring, while mature adults become bright yellow. Their morphology also changes, with gregarious adults developing longer wings suited for migration. This transformation from a lone insect to a social creature sets the stage for destructive swarms.
Formation and Behavior of Swarms
Once locusts have entered the gregarious phase, they begin to act in unison, leading to the creation of massive swarms. The process starts with the wingless nymphs, or hoppers. These young locusts form dense groups called “hopper bands” that march across the ground, consuming vegetation in their path.
As the hoppers mature into winged adults, they aggregate into flying swarms. These swarms can contain anywhere from 40 to 150 million locusts per square kilometer. A single swarm can cover hundreds of square kilometers, appearing as a dark, moving cloud that can obscure the sun.
The behavior of these swarms is largely dictated by the wind. They travel with the prevailing currents, which allows them to cover vast distances, sometimes up to 150 kilometers in a single day. This migratory capacity enables them to cross countries and even continents, moving from depleted areas to new regions with fresh vegetation in a relentless search for food.
Agricultural and Economic Impact
A desert locust invasion severely affects agriculture and food security, as swarms are voracious feeders that consume nearly any green vegetation, including crops, pastureland, and fodder. A very small swarm can eat the same amount of food in one day as approximately 35,000 people. This intense feeding can lead to total crop loss in a matter of hours.
The 2003-2005 plague in West Africa caused an estimated $2.5 billion in crop damage. More recently, the upsurge in East Africa and Yemen in 2020 was projected to cause damages and losses of up to $8.5 billion. These figures represent not just lost harvests but also the long-term disruption of livelihoods for farmers and pastoralists who depend on the land for survival.
Regions most vulnerable to these impacts include the Horn of Africa, the Middle East, and Southwest Asia, where agriculture is often the backbone of the economy. In agriculturally dependent countries like Mali and Niger, widespread crop damage can be disastrous for national economies and individual households. The destruction of pastureland also threatens the survival of livestock, a source of income and food for many communities.
Monitoring and Control Strategies
Responding to the threat of desert locusts relies on preventative control, focusing on early warning and rapid reaction. This approach is coordinated internationally by organizations like the Food and Agriculture Organization (FAO) of the United Nations. The FAO’s Desert Locust Information Service (DLIS) monitors weather patterns, ecological conditions, and locust populations across 60 countries to forecast the development of swarms.
Effective monitoring combines satellite data with on-the-ground surveys. Satellites help identify areas of recent rainfall and green vegetation, which are potential locust breeding grounds. Field teams are then dispatched to these remote locations to confirm the presence of locusts and assess their developmental stage and density. The goal is to detect and control hopper bands before they develop wings and form mobile swarms, as this is when they are most vulnerable and concentrated.
Control operations primarily involve the targeted application of pesticides. Vehicle-mounted and aerial sprayers are used to deliver small, concentrated doses of chemical agents to kill the locusts. In recent years, there has been a growing emphasis on biopesticides, which are based on natural fungi that infect and kill locusts, as a more environmentally friendly alternative. Success depends on timely intervention and cooperation between affected countries to manage this transboundary pest.