What Is the Red Locust and Why Is It a Threat?

The red locust, Nomadacris septemfasciata, is one of sub-Saharan Africa’s most damaging migratory pest insects. Found across a vast range from Madagascar to southern and eastern Africa, it poses a recurring agricultural threat because of its ability to transform from a harmless solitary grasshopper into a swarming, crop-destroying plague. That transformation is driven by population density, weather patterns, and, increasingly, human land-use changes, making the red locust a problem that sits at the intersection of ecology, climate, and food security.

A Grasshopper With Two Personalities

At low population densities, the red locust behaves like an ordinary grasshopper. It lives alone in grasslands and floodplains, feeds modestly, and avoids other individuals. In this solitary state it is greenish or straw-colored and relatively inconspicuous. But when conditions cause populations to crowd together, the insects undergo a dramatic shift in behavior, physiology, and appearance. They become gregarious: darker in color, more active, and inclined to aggregate into bands of nymphs and eventually into flying swarms of adults that can travel hundreds of kilometers.

This switch is not a simple on-off toggle. Research on red locust nymphs in Madagascar showed that pigmentation changes track population density in a graded way, moving through several intermediate “transiens” stages between fully solitary and fully gregarious forms.

The color shift is a visible warning sign: field scouts monitoring red locust populations can use nymph coloration as an indicator of how close a population is to gregarizing. Once the transition to full gregarious behavior is complete, the locusts begin marching as hopper bands and later take to the air in coordinated swarms.

Where Red Locusts Breed and Swarm

Red locusts are native to sub-Saharan Africa and Madagascar. Their range stretches from South Africa northward through Zambia, Malawi, Mozambique, Tanzania, and into parts of the Democratic Republic of Congo. Madagascar hosts its own populations, which follow seasonal migration routes on the island.

The species does not breed everywhere it occurs. Instead, it concentrates its egg-laying in specific “outbreak areas,” typically large floodplains or lake basins where seasonal flooding creates expanses of tall grass. The most historically important outbreak areas on the African mainland include the Rukwa Valley in western Tanzania, the plains around Lake Chilwa in Malawi, and the Mweru wa Ntipa flats in northern Zambia. In Madagascar, solitary red locusts breed in lower-elevation areas that receive moderate seasonal rainfall, then migrate to higher-elevation refuge areas during the dry season.

These outbreak areas act like incubators. When conditions are right, locust numbers build rapidly in these concentrated habitats, and once the population crosses a density threshold, swarms form and spread outward into surrounding agricultural regions. A single outbreak area can seed swarms that affect multiple countries, which is why red locust control has always been a regional problem rather than a national one.

The Annual Life Cycle

Red locusts produce a single generation per year, with their life cycle tightly synchronized to the wet and dry seasons. In Madagascar, and similarly in mainland Africa, mating and egg-laying happen at the start of the rainy season in November and December. Females dig into the soil and deposit egg pods, with clutch sizes ranging from about 20 to 100 eggs for gregarious females and up to nearly 200 eggs for solitary ones.

Eggs incubate for roughly 24 to 36 days before hatching. The nymphs, called hoppers, then develop through six molts in the gregarious phase or seven in the solitary phase, a process that takes about 50 to 70 days. By March or April, new adults emerge and spend about ten days hardening their exoskeletons before entering a reproductive pause, or diapause, that carries them through the dry season from May through October. When the rains return in November, the adults migrate back to breeding areas, mate, lay eggs, and the cycle begins again.

This annual rhythm creates a narrow but critical window for control. Once swarms have formed and adults are airborne, they are extremely difficult to contain. The most effective interventions target hopper bands during the weeks between hatching and fledging, while the insects are still on the ground and relatively concentrated.

How Climate and Flooding Set the Stage

Whether red locust numbers build to outbreak levels in any given year depends heavily on local weather, particularly rainfall and flooding patterns. A long-running study of the Rukwa Valley outbreak area in Tanzania found that the relationship between rain and locusts is not straightforward. Very high levels of Lake Rukwa are associated with small locust populations, likely because extensive flooding drowns eggs and eliminates the grassland habitat hoppers need. But when the lake is not unusually high, locust numbers are negatively linked to total rainfall from two wet seasons earlier, meaning that heavy rains in one year tend to suppress population growth about two years later.

The size of the preceding adult population also matters. A larger parental population at oviposition time predicts more hoppers the following season, as you might expect. And there is suggestive evidence that early-season rainfall in October through December has a positive effect on hatching success, possibly because it provides the soil moisture eggs need to develop.

What this means in practical terms is that red locust outbreaks are not random. They tend to follow specific sequences of wet and dry years. A period of moderate flooding that keeps grasslands lush without drowning the eggs, followed by favorable early-season rains, creates ideal breeding conditions. Consecutive good breeding seasons allow populations to build until crowding triggers the phase change into gregarious behavior. Understanding these climate signals is central to early warning systems, because by the time swarms are visible, the damage has already begun.

Why Swarms Are So Destructive

A solitary red locust nibbling grass on a floodplain is not a threat to anyone’s livelihood. A gregarious swarm is a different creature entirely. Swarms can contain millions of individuals, and a large swarm can strip a field of grain, maize, or sorghum in hours. Red locusts are generalist feeders that consume grasses and cereal crops readily, which makes them a direct threat to staple food production across eastern and southern Africa.

The damage is amplified by the scale of movement. Once airborne, swarms can cover substantial distances on prevailing winds, spreading far beyond the outbreak areas where they originated. A swarm that forms in Tanzania’s Rukwa Valley can eventually reach cropland in Zambia, Malawi, or Mozambique. Because many of the affected regions depend heavily on rain-fed subsistence agriculture, even a partial crop loss can translate into food shortages for communities with little economic buffer.

Historical plague periods illustrate the scale of the problem. The red locust was responsible for devastating plague cycles across southern Africa during the first half of the twentieth century, prompting the formation of the International Red Locust Control Organisation for Central and Southern Africa (IRLCO-CSA) in 1970. This intergovernmental body, headquartered in Zambia, coordinates surveillance of outbreak areas and mounts rapid-response control operations when hopper bands or early swarms are detected. The creation of a dedicated multinational agency for a single insect species reflects how seriously the threat has been taken.

How Deforestation Is Opening New Fronts

Climate has always shaped red locust outbreaks, but human land-use changes are altering the geography of the threat. In Madagascar, satellite imagery analysis revealed that deforestation between 1986 and 2004 opened up three previously unknown migration pathways for red locusts. Before the forest was cleared, these corridors were inaccessible, blocking locusts from reaching certain egg-laying zones. Once the trees were gone, the insects could move through the cleared land, access new oviposition areas, breed in higher numbers, and concentrate enough to undergo gregarization.

⁴

This finding is alarming for several reasons. It means that the traditional outbreak areas entomologists have monitored for decades may no longer capture the full picture of where red locust populations can build. New breeding sites can emerge as forest is converted to farmland or pasture, and these sites may go unmonitored simply because nobody expected locusts there. In a region where deforestation continues at a significant pace, the potential for surprise outbreaks in previously safe areas is growing.

Remote sensing technology, including satellite imagery and digital elevation models, has become an important tool for identifying these landscape changes before they translate into locust crises. The same satellite data that revealed the new corridors in Madagascar is now part of the broader toolkit for locust surveillance, helping researchers map habitat suitability and predict where populations might concentrate.

⁴

Monitoring and Control Strategies

Red locust management rests on a principle that sounds simple but is logistically demanding: find the hopper bands before they become flying swarms, and eliminate them on the ground. IRLCO-CSA maintains field teams that conduct regular ground surveys of known outbreak areas during the breeding season, counting nymphs, assessing color phase, and estimating population density. When populations cross threshold levels, control teams deploy insecticides, typically by vehicle-mounted sprayers or aircraft, to kill hopper bands before fledging.

This preemptive approach works well when funding and access allow consistent surveillance. During periods of political instability, conflict, or budget shortfalls, monitoring gaps open up, and locust populations can build undetected. The Rukwa Valley, for instance, is remote and difficult to access during the wet season, exactly when monitoring matters most. Similar challenges exist at other outbreak areas. A missed breeding season can mean the difference between a manageable local buildup and a regional plague.

Chemical control remains the frontline tool, but it carries environmental costs. Broad-spectrum insecticides used against locusts also kill non-target insects, including pollinators and natural predators that would otherwise help keep locust numbers in check. There has been growing interest in biopesticides, particularly formulations based on the fungus Metarhizium acridum, which infects and kills grasshoppers and locusts while posing far less risk to other organisms. Adoption of biopesticides has been slow, partly because they act more slowly than chemical alternatives and partly because of cost and availability challenges in the rural areas where they are most needed.

Red Locusts Compared to Other Plague Locusts

Africa is home to several locust species capable of forming plagues. The desert locust, which operates across the Sahel and into the Middle East and South Asia, tends to grab international headlines because its swarms can be enormous and its range spans dozens of countries. The red locust’s range is more restricted to eastern and southern Africa and Madagascar, and its outbreaks, while devastating locally, have historically received less global media attention.

The ecological triggers also differ. Desert locust outbreaks are closely tied to rainfall events in arid zones, where sudden vegetation growth after rain provides food for rapid population buildup. Red locust outbreaks are more closely linked to the flooding dynamics of specific floodplains and lake basins, making them somewhat more geographically predictable but also more sensitive to changes in hydrology. The brown locust of southern Africa occupies yet another niche, breeding in semi-arid Karoo landscapes and following its own distinct plague cycle.

What all these species share is the capacity for phase change, that density-dependent switch from solitary to gregarious behavior. But the specific environmental triggers, the timing, and the geography are different for each species, which means that control strategies and early-warning systems need to be tailored to the particular biology of each one. A surveillance network designed for desert locusts in the Sahel would miss the floodplain dynamics that drive red locust outbreaks in Zambia or Tanzania.

The Role of Climate Change

Climate projections for eastern and southern Africa suggest shifts in rainfall patterns, including changes in the timing and intensity of wet seasons, rising average temperatures, and more frequent extreme weather events. For the red locust, any of these changes could alter the delicate balance of flooding and drying that determines breeding success in outbreak areas.

If seasonal rains arrive earlier or later than the historical norm, the synchronization between egg-laying, hatching, and vegetation growth could be disrupted in ways that either suppress or amplify locust numbers. More intense rainfall events could cause the kind of extreme flooding that drowns eggs, or, if followed by rapid drying, could create exactly the mosaic of wet grassland and exposed ground that red locusts favor for oviposition. The honest answer is that the specific effects of climate change on red locust dynamics are difficult to predict with confidence, because the system involves multiple interacting factors with lagged effects spanning two or more years.

What is clear is that the historical climate records that underpin current early-warning models may become less reliable guides to future outbreaks. The correlations between rainfall, lake levels, and locust numbers documented in the Rukwa Valley, for example, were established using data from the mid-twentieth century onward.

If the underlying climate regime shifts substantially, those historical relationships could weaken, leaving forecasters with less predictive power at exactly the time it is most needed. Integrating real-time satellite data on vegetation, soil moisture, and water levels into forecasting models is one way researchers are trying to maintain accuracy as conditions change.

Red Locusts as Food

Across much of Africa, grasshoppers and locusts have been part of human diets for centuries. Red locusts are no exception. When swarms descend, people in affected communities often collect and eat the insects, which are high in protein and fat. They are typically roasted, fried, or dried for preservation. In some areas, locust harvesting during an outbreak is both a food source and an informal pest-control measure, reducing local swarm density while supplementing diets.

There is growing academic and commercial interest in edible insects as a sustainable protein source, and locusts frequently appear in those discussions. For communities facing crop destruction from a swarm, the ability to harvest and consume the very insects destroying their fields offers a small but meaningful form of resilience. The catch, of course, is that swarms treated with insecticides are unsafe to eat, which creates tension between chemical control operations and traditional harvesting practices. This is another argument in favor of biopesticides, which pose fewer food-safety concerns for communities that consume the target insects.

1
Psyche: A Journal of Entomology. Phase-Dependent Color Polyphenism in Field Populations of Red Locust Nymphs (Nomadacris septemfasciata Serv.) in Madagascar
2
Journal of Orthoptera Research. Ecology and Population Dynamics of Solitary Red Locusts in Southern Madagascar
3
Bulletin of Entomological Research. The Effect of Climate and Weather on the Numbers of the Red Locust, Nomadacris septemfasciata (Serv.), in the Rukwa Valley Outbreak Area
4
ScienceDirect. Land Surface Remote Sensing – Chapter 8 – Applications of Remote Sensing to Locust Management