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What Caused African Migratory Locusts to Swarm?

Africa is currently experiencing two locust outbreaks both due to unusual climatic conditions. These two outbreaks are unrelated but are due to the unusually high rainfall and flooding in the areas where low densities of the locusts occur. The desert locust (Schistocerca gregaria) is producing a plague type outbreak in North and East Africa. This outbreak started in June 2019 and the threat is still there. Then there are localised swarms of the African migratory locust (Locusta migratoria migratorioides) in southern Africa. Two other locust species – the red locust (Nomadacris septemfasciata) and the brown locust (Locustana pardalina) – are known to have swarmed and caused agricultural damage in southern Africa. Locusts are grasshoppers that have the potential to form a swarm of thousands to hundreds of thousands of individuals. They undergo phase polymorphism, which means that they can change from a solitary form into a gregarious form – meaning they congregate in large numbers. These have a different colour and different behaviour. The solitary form is scattered and blends into the environment. The gregarious form arises from an increase in population density which causes the locusts to aggregate. Locusts need to multiply, concentrate and aggregate for swarms to form.