Desert Locust (Schistocerca gregaria): Facts, Swarms and Plagues

What does a desert locust look like?

The desert locust is a typical short-horned grasshopper, with short, stout antennae, large compound eyes, chewing mouthparts and long, powerful hind legs for jumping. Its leathery forewings fold over the abdomen and reach beyond its tip, and its clear, gauzy hindwings open like fans in flight. Adults are about 4.5–9 cm (1.8–3.5 in) long, and females are larger than males.

What makes the species remarkable is that its color, shape and behavior depend on how crowded it is. This is called phase polyphenism: the same genes produce different forms under different conditions.

Gregarious adults also have a slightly different body shape, with a saddle-shaped pronotum (the shield behind the head), and they tend to be somewhat smaller than solitary adults.

Solitary and gregarious phases

Most of the time desert locusts live at low density, scattered across vast deserts, and few people notice them. When good rains fall after a drought, plants spring up and locusts breed quickly. As the vegetation dries out again, the growing population is squeezed into the remaining green patches.

In these crowded conditions, locusts keep bumping into each other. Repeated touching of the hind legs raises the level of serotonin, a signaling chemical, in the nervous system, and within a few hours a solitary locust starts to behave gregariously: it seeks out other locusts instead of avoiding them. Over the following days and generations the insects change color, shape and physiology. The full story, and how a few bands grow into a plague, is explained in why do locusts swarm?

The change is reversible. When crowded locusts are kept apart, they drift back toward the solitary form, although this usually takes one or more generations.

Habitat and range

In quiet years, called recessions, desert locusts live in a belt of about 16 million square kilometers (6.2 million square miles) of desert and semi-desert. It stretches from Mauritania across the Sahara and the Sahel, through the Arabian Peninsula and Iran, to the deserts of Pakistan and northwest India. They need sandy or silty soil to lay eggs, and fresh green plants for the young.

During plagues, swarms can spread over about 29–32 million square kilometers (11–12 million square miles), roughly a fifth of the world’s land surface, and affect up to 60 countries. Swarms have reached as far as Spain and the Canary Islands, Kenya, Tanzania and the Himalayan foothills. A second, smaller subspecies, S. g. flaviventris, lives in the dry southwest of Africa.

Diet: what desert locusts eat

Desert locusts are herbivores and eat almost any green plant. Biologists call them polyphagous, meaning they feed on many kinds of plants. They chew leaves, shoots, flowers, fruit, seeds and even bark, and they attack crops such as millet, sorghum, maize, wheat, barley, rice, cotton, vegetables, date palms and fruit trees.

An adult eats roughly its own body weight of fresh plants each day, about 2 g (0.07 oz). That sounds tiny, but a swarm contains millions of locusts in every square kilometer. FAO estimates that a swarm covering 1 square kilometer can eat as much food in a day as about 35,000 people. For how this compares with ordinary grasshoppers, see what do grasshoppers eat?

Swarms and how far they fly

Gregarious hoppers, which cannot yet fly, gather in dense bands that march across the ground. After the final molt the winged adults form swarms. Typical swarms hold about 40–80 million locusts per square kilometer, and dense ones may hold more than 100 million. A single swarm can cover anything from less than 1 square kilometer to several hundred, and in early 2020 one swarm in northern Kenya was reported to measure about 40 by 60 km (25 by 37 mi).

Swarms fly by day and drift downwind, usually covering about 100–150 km (60–95 mi) a day. They rarely fly higher than about 2,000 m (6,600 ft), where the air becomes too cold, so tall mountain ranges such as the Atlas and the Himalayas act as barriers. Swarms regularly cross the Red Sea, and in October 1988 swarms from West Africa crossed the Atlantic Ocean and reached the Caribbean in about ten days.

Like other grasshoppers, a desert locust can also jump. A large locust can leap up to about 1 m (3 ft 3 in) using stored energy in its hind legs, as described in how far can a grasshopper jump?

Reproduction, life cycle and lifespan

The desert locust goes through three stages: egg, hopper (nymph) and winged adult. There is no pupa; each hopper molts five or six times, looking more like an adult after each molt.

After mating, the female probes moist, sandy soil with the tip of her abdomen and digs a hole about 10 cm (4 in) deep. She lays an egg pod of several dozen to more than 100 eggs, surrounded by foam that hardens and plugs the hole. Gregarious females usually lay fewer eggs per pod than solitary ones. A female may lay two or three pods during her life.

The eggs hatch in about two weeks in warm conditions, or much longer in cold weather. Hoppers take roughly 5–6 weeks to reach adulthood, and young adults then need from 2–4 weeks to as long as 6 months to become sexually mature, depending on rain and temperature. With good conditions there can be two to five generations a year, and numbers can rise about 10 to 16 times from one generation to the next.

In total, a desert locust lives about 3–6 months in total, from hatching to death. Most of that time is spent as an adult, and adults may live longer when dry, cool weather delays maturation. The species survives harsh dry periods mainly as eggs and as scattered solitary adults.

Predators and natural enemies

Desert locusts are eaten by many animals. Birds such as storks, kites and bee-eaters, lizards, and small mammals hunt them, and predatory and parasitic wasps, flies and beetle larvae attack their eggs and hoppers. These enemies help keep solitary populations in check, but they cannot keep up with the enormous numbers in a swarm. A swarm passing through often creates a feast for birds.

Plagues and upsurges in history

Locust plagues appear in some of the oldest written records. The Book of Exodus describes locusts as the eighth plague of Egypt, and the desert locust is the most likely species behind such accounts. In 1915 swarms stripped much of the vegetation in and around Palestine, Lebanon and Syria.

Major desert locust plagues in the 20th century included 1926–1934, 1940–1948, 1949–1963, 1967–1969 and 1987–1989. A large upsurge (a sharp rise that falls short of a full plague) hit West Africa in 2003–2005.

The most recent major event was the 2019–2022 upsurge. Heavy rain from two cyclones in 2018 allowed several generations of breeding in the remote Empty Quarter of the Arabian Peninsula. Swarms then spread to Iran, Yemen, India and Pakistan, and crossed into the Horn of Africa. Kenya saw its worst invasion in about 70 years, and Ethiopia and Somalia their worst in about 25 years. International monitoring and large-scale treatment brought the upsurge under control by early 2022.

Conservation status

The desert locust has not been assessed by the IUCN, so its Red List category is Not Evaluated. Its numbers rise and fall enormously from year to year, and it is in no danger of extinction. Instead, the UN Food and Agriculture Organization (FAO) runs a Desert Locust Information Service that tracks rainfall, vegetation and locust reports from field teams, and issues forecasts and warnings to the countries at risk.

Myths and facts

Myth: locusts and grasshoppers are different kinds of insect. In fact, every locust is a grasshopper. “Locust” is simply the name for the few grasshopper species, about a dozen to twenty worldwide, that can change phase and swarm.

Myth: swarms appear out of nowhere. The insects were there all along in small numbers. Swarms build up over several generations after unusually good rains, which is why early warning based on rainfall and field surveys works.

Relationship with people

For farmers and herders in Africa and Asia, desert locusts can be a disaster, destroying crops and pasture in a few hours and threatening the food supply of millions of people. At the same time, locusts are eaten in many countries, roasted or fried, and are a rich source of protein. The desert locust is one of the locusts traditionally considered kosher in some Jewish communities of the Middle East.

Scientists also study the desert locust in laboratories. It has helped researchers understand insect flight, muscle and nerve function, and how crowding can change an animal’s body and behavior. To see how it compares with its singing relatives, read grasshopper vs cricket.