Desert Locust (Schistocerca gregaria)

InsectOrthopteranSwarming

Overview

The desert locust (Schistocerca gregaria) is a grasshopper — but one with an extraordinary property. A locust is not a separate kind of insect from a grasshopper; it is a grasshopper species capable of switching between two entirely different forms.

In its solitary phase the desert locust is a shy, green or sandy, cryptically coloured insect that avoids others of its kind. When crowding triggers the change, it enters the gregarious phase: the insects turn yellow and black, become stockier, grow longer wings, become far more active, and actively seek each other out.

The trigger is remarkably specific — repeated contact, particularly touching of the hind legs, as animals are pushed together on shrinking patches of vegetation after rain. The transformation is called phase polyphenism, and it turns a harmless insect into the basis of a swarm.

Habitat & Range

Desert locusts inhabit dry and semi-arid regions across North and West Africa, the Sahel, the Arabian Peninsula and into southwest Asia. In the solitary phase they live at low density across a vast area of desert and scrub. Rainfall drives the cycle: good rains produce a flush of vegetation, allowing rapid breeding, and as that vegetation dries the insects are forced together, which sets the phase change in motion.

Diet

Desert locusts are herbivores that feed on a wide range of green plants — leaves, shoots, stems, flowers, seeds and bark. It is this generalist appetite combined with swarm density that makes them agriculturally significant, since a swarm consumes vegetation without regard to whether it is crop or wild plant.

Behavior

Phase change is the defining behaviour. Gregarious nymphs form dense marching bands on the ground; winged adults form swarms that can travel long distances on the wind, crossing seas and deserts. Solitary-phase locusts, by contrast, are nocturnal, cryptic and actively avoid each other. The change is reversible: as densities fall, subsequent generations revert toward the solitary form.

Human Interaction & Conservation

The desert locust is one of the most economically significant insects in the world, and locust plagues are documented across thousands of years of history in the regions it occupies. Modern management focuses on monitoring breeding areas after rainfall and intervening early, coordinated internationally, because a swarm is far harder to address than an emerging outbreak. This profile is educational and offers no pest-control, pesticide or treatment guidance — such matters are handled by national plant protection authorities and international agencies.