Desert locust

What you are looking at

Vegetation and crops stripped down to bare stems across an area that can run to hundreds of square kilometres, following the arrival of a dense, low, moving cloud of flying insects, sometimes visible from a considerable distance and audible as a mass before it is seen. A single adult eats roughly its own weight in a day, and a swarm can hold tens of millions of individuals per square kilometre, so the scale of loss bears little resemblance to ordinary grasshopper damage.

What crowding does to this insect is what makes it exceptional. For most of the time it lives as a solitary insect, pale brown, well camouflaged and easily overlooked, doing no more damage than any other grasshopper. When conditions concentrate enough individuals together, typically after rain breaks a drought and vegetation flushes across a breeding area, a genuine change in colour, behaviour and biology follows. Nymphs turn pink to grey-brown and march together in dense bands across the ground before they can fly, and adults mature into a yellow-and-black gregarious form that forms and travels in swarms. The marching hopper bands are usually the first visible sign a local outbreak is developing, well before any swarm takes to the air.

The most destructive migratory pest on earth

At its full extent the invasion area covers around 29 million square kilometres across North and West Africa, the Arabian Peninsula, the Middle East and south-west Asia as far as the Indian subcontinent, and during a major upsurge the areas affected can reach a fifth of the world’s land surface and threaten the livelihoods of more than 60 of the world’s poorest countries. Southern Europe, including the Iberian Peninsula, the Canary Islands and Madeira, sits at the extreme margin of the historical range and has recorded rare incursions, though it is not part of the area affected in a typical year, and the pest has never established in the Americas, Australia, New Zealand or the wider Pacific.

Because outbreaks develop from remote breeding areas that can span several countries at once, the Food and Agriculture Organization has run a continuous early warning system, the Desert Locust Information Service, since 1978, tracking breeding conditions worldwide and issuing forecasts up to six weeks ahead. That lead time, combined with organised survey and control operations reaching a hopper band before it can fly, is what has kept most seasons from developing into a full plague.

What to do about it

Report a hopper band or a swarm to the national locust control unit or FAO immediately, since early detection is what lets a developing outbreak be controlled while it is still localised.

Cooperate with organised survey and control operations in an affected area, since effective control happens at a regional and national scale rather than field by field.

On a small local outbreak, trenches or physical barriers can trap and allow the destruction of a still-flightless hopper band, though this does not scale to a widespread plague.

Support fungal biopesticide campaigns run by national and regional locust control organisations as the preferred response once a swarm has formed. Coordinated chemical spraying by trained control units remains a last resort reserved for a plague at a scale biopesticide alone cannot contain, and it stays a decision for those organisations rather than something an individual grower undertakes.