What You Need to Know About Locust Swarms

First published in Sanctuary Asia, Vol. 40 No. 5, May 2020

By Lakshmy Raman

Whirring wings have taken over the news cycle. Reports, videos and images of locust swarms in Western and Central India are being widely circulated causing much alarm. But much of the information that is being circulated and causing panic is false, or misguided. 

How do locust swarms occur?

The desert locust Schistocerca gregaria is found in the desert and scrub regions of Northern Africa, the Sahel (Burkina Faso, Chad, Mali, Mauritania, and Niger), the Arabian Peninsula and parts of Asia like Western India. Locust plagues find reference even in the Bible. Published accounts of locust invasions in North Africa date back to AD 811.

Locust populations generally multiply in vast, uncontrolled numbers after prolonged periods of drought. Various studies have shown that changing weather patterns caused by climate change have worsened drought and floods over the past decade. The starting point of the current locust plague, according to scientists, was in 2018, when cyclones dumped large amounts of rain in locusts’ breeding grounds in the Arabian Peninsula, which includes parts of Saudi Arabia, Oman, UAE and Yemen, creating optimal breeding conditions. The storms filled a vast desert area known as the Empty Quarter with freshwater lakes, inducing lush vegetation to grow in a usually barren environment. These new conditions attracted desert locusts hunting for food; inevitably, they laid their eggs in the sand. Hatching occurs when the soil is moist. The larvae mature in two weeks, and can then start reproducing. The plentiful food supply resulted in rapid multiplication of locusts in just a few months. The subsequent mild winter was an added bonus for the locusts; the weather did little to impact populations, which managed to survive in large numbers.

Competition for food can influence locusts’ behaviour – usually solitary, they can become gregarious. This change occurs over two or three generations, until subsequently, dense bands of flightless nymphs and swarms of winged adults are formed, which can be devastating to agriculture. These biphasic insects are drab brown in their solitary form and electric yellow in gregarious form. Parvish Pandya, Head, Natural History, Photography and Science, Sanctuary Asia, provided this insight – “Earlier scientists had thought that the two (solitary and gregarious) are different species and had named them as Schistocerca solitaria and S. gregaria, a fact that was disproved since it’s the same species, which in special conditions turns from solitary to gregarious phase”.

From the Arabian Peninsula, the swarms crossed the Red Sea to the coast of Somalia in the summer of 2019 and laid more eggs there before moving west and south, deeper into Africa. The swarms first arrived in the Horn of Africa at the end of summer 2019. The Indian Ocean Dipole (difference in temperature between the western and eastern Indian Ocean waters) impacted weather conditions and more cyclones and rain in East Africa allowed locust populations to increase. The Horn of Africa experienced eight cyclones in 2019! By autumn, the locusts had spread inland from Somalia and Ethiopia to Kenya and Uganda and by early 2020, into Eritrea, Sudan, Democratic Republic of Congo and Tanzania. Some swarms also moved from the Arabian Desert into the Middle East and then further into Pakistan and India.

How can locust swarms be controlled?

A single swarm can range from small (hundreds of square metres) to huge, comprising billions of locusts that may cover an area of more than 1,000 square kilometres. In a day, a locust swarm can fly 100 km. in the direction of prevailing winds. Bands of nymphs can move about 1.5 km. each day. 
These locusts can eat the equivalent of their body mass each day (two grammes) in vegetation. This includes leaves, flowers, bark, stems, fruit, and seeds. They feed on nearly all crops, and even non-crops.

The locust’s natural enemies include predatory and parasitic wasps and flies, predatory beetle larvae, birds, and reptiles. In some countries, locusts are eaten dried, fried, boiled or grilled. However, the most commonly used control strategy is the spraying of pesticides from airplanes. Many of the countries that have been impacted in Africa lack the resources to carry out large-scale operations. The locust invasion has been a double whammy for countries in Africa that have been reeling under droughts and bad harvests and in some cases, war. The outbreak seen in Ethiopia and Somalia in 2019 was the largest in more than two decades.

Pesticide use, of course, also brings with it environmental implications. These could adversely impact other wildlife as well and affect soil and water resources. Another compounded issue is that due to pesticide overuse resulting in biomagnification, several insectivorous bird populations that served as a natural control to pests, have been decimated.

What are the most effective solutions? Being proactive against localised outbreaks before it reaches plague status is vital. For this, there must be early detection of bands and swarms, particularly in breeding areas. Locust control must also take place before they become gregarious (and start swarming in unfathomable numbers), when locusts are in non-reproductive nymphal stage. 

Current research on locusts is focused on early warning and detection including remote sensing, GIS technologies, understanding locust behaviour and population dynamics, and use of radar aircraft to locate swarms.

The link between locust swarms and climate change

Scientists studying the difference between average sea-surface temperatures in the western and eastern Indian Ocean explain that when temperatures are higher in the western Indian Ocean, it is referred to as a positive dipole phase. This positive dipole phase occurred four times in a 30 year period in the early 20th century, but between 1989 and 2009, this increased to 10 times. This means that the western Indian Ocean near Africa is warming at a rapid rate, faster than the eastern Indian Ocean, leading to a large temperature difference and subsequently, more cyclones and rain in the western region. The Indian Ocean dipole has also been linked to the bushfires in Australia.

Even if global temperature rise is limited to 1.5°C – the target set by the Paris Agreement – positive dipole events could still double, say scientists. A warming climate will only result in more cyclones and more such pest outbreaks.

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