The common perception of a locust plague suggests an invading force, but the reality is more complex than a simple non-native takeover. Locusts are not typically classified as invasive species in the way that term is used in ecology. Instead, they are native organisms with a unique biology that allows them to transform from harmless individuals into devastating, migratory swarms. The destruction they cause is a consequence of a dramatic behavioral and physiological shift within their established home range.
Defining the Ecological Status
An invasive species is defined as an organism that is non-native to an ecosystem and whose introduction causes economic or environmental harm. Locusts, conversely, are native to the regions they devastate, like the African Sahel or the Middle East. They are more accurately described as native pests, whose harmful impact stems from an explosive, localized population increase within their natural distribution area. The Desert Locust (Schistocerca gregaria), for example, is endemic to the arid and semi-arid regions it inhabits during quiet periods. The problem arises when environmental conditions trigger a mass outbreak, changing a species that is an established part of the local ecology into a destructive force.
The Biology of Swarming
The mechanism that transforms a solitary grasshopper into a destructive locust is a process called phase polyphenism. This is a complete biological and behavioral shift. The insects exist in two states: the solitarious phase, where they are shy, camouflaged, and avoid each other, and the gregarious phase, where they become social, brightly colored, and migratory.
The transformation is initiated by specific environmental and physical triggers. Heavy rainfall followed by a rapid growth of vegetation creates ideal conditions for successful breeding and high population densities. As the young locusts, called hoppers, become crowded, repeated physical contact on their hind legs triggers a surge of the neurotransmitter serotonin in their nervous system. This chemical cascade acts like a switch, fundamentally altering the insect’s behavior. The newly gregarious insects then form dense, marching bands of nymphs and, eventually, flying swarms of adults that move as a single unit.
Global Range and Major Outbreak Zones
The most globally recognized and destructive species is the Desert Locust, which occupies a vast area from West Africa, across the Arabian Peninsula, and into South Asia. During quiet periods, their recession area covers about 16 million square kilometers across 30 countries. Plagues, however, can cause their range to expand dramatically, potentially covering up to 29 million square kilometers over parts of 60 countries, which is more than 20% of the world’s land surface.
Another significant species is the African Migratory Locust (Locusta migratoria), which affects large parts of Africa and Asia. The historical example of the Rocky Mountain Locust (Melanoplus spretus) in North America illustrates the catastrophic potential of these insects. This species, now extinct, once formed a single swarm in 1875 estimated to be 510,000 square kilometers in size, the largest concentration of animals ever recorded.
Controlling Outbreaks
Modern locust management focuses heavily on a preventive control strategy to stop outbreaks before they develop into full-scale plagues. This involves continuous surveillance and early warning systems across the vast recession areas. International organizations like the Food and Agriculture Organization (FAO) coordinate monitoring efforts across affected countries, using tools that integrate field data with satellite imagery and weather analysis.
Proactive monitoring utilizes satellite-based data to identify areas with rainfall and vegetation growth, which are prime breeding grounds for the insects. Field teams use mobile geospatial applications and unmanned aerial vehicles (drones) to confirm the presence of high-density populations. The primary control method is the targeted application of insecticides, typically applied to the non-flying hopper bands to prevent the formation of swarms. In sensitive ecosystems, biopesticides based on fungal pathogens, such as Metarhizium acridum, are encouraged as an environmentally conscious alternative to chemical control.