Swarms of locusts the size of entire cities have invaded more than 15 countries across East Africa, the Middle East and Asia, devastating crops.
A swarm of 70 billion flying insects covering 740 square kilometres. More than four times the size of the urban area of Milan and almost equal to that of Rome: this is how large a single locust swarm can grow. It sounds like an apocalyptic scene from the plagues chapter of the Bible — yet for many countries on the Arabian Peninsula and in East Africa, it is reality. An invasion is afflicting the entire region, from Oman to Kenya: it is devastating crops, decimating pastures, threatening the food supply of tens of millions of people and aggravating the food crisis. These swarms, as large as entire cities, sow chaos, descend on farmland and devour everything within a matter of hours. To date, the crisis has struck more than fifteen countries across East Africa, the Middle East and Asia.
But how do locust swarms form? Which are the most vulnerable areas? Why are the consequences of these invasions so brutal? What dangers face those whose land is swept by a passing swarm?
Let us take a step back.
Locusts are close relatives of grasshoppers and the two insects look very similar. However, the behaviour of the former is entirely different. Locusts are distinguished by their ability to shift from a solitary state — in which each individual actively avoids others — to a social state, known as "gregarious", in which masses of flying locusts darken the sky. Always in search of food, solitary locusts are forced to cluster together during periods of drought, when vegetation dies and leaves only a few green areas in deserts, their natural habitat. At this stage, a sudden transformation takes place.
Within a few hours of crowding, a hormone — serotonin — stimulated in locusts by hairs on their legs and by the sight and smell of other individuals, is released in large quantities. In the central nervous system, serotonin triggers behavioural changes: faster movement, increased sociability and a heightened appetite. With the return of rainfall and moister growing conditions, new generations of locusts form groups that forage in unison. This is where the fundamental transition occurs: wings grow and the insects transform from hoppers into bright yellow locusts.
The shift from the solitary to the gregarious state also affects the locust's physiology: the brain grows larger and the legs become shorter. Within swarms, there is also an increase in resilience: the offspring of gregarious locusts develop smaller legs, their jumps are shorter, but they manage to use less energy to cover the same distance.
The desert locust is the species with the greatest economic impact in terms of the damage it causes, and it threatens one fifth of the Earth's land surface and one tenth of the global population. The last major invasion dates back to 1986, when it struck North Africa and the Middle East for three long years until 1989.
Carried by the wind, desert locusts fly at a speed of around 16–19 kilometres per hour. Swarms can travel up to 130 kilometres or more in a day and can remain airborne for extended periods, regularly crossing stretches such as the Red Sea — a distance of 300 kilometres. In the past there have been long and spectacular migrations of swarms that travelled from north-west Africa to the British Isles in 1954 and, in 1988, from West Africa to the Caribbean, a distance of five thousand kilometres in around ten days. Solitary desert locusts usually fly at night, while gregarious adults (swarms) fly during the day.
During quiet periods (known as "recessions"), desert locusts are confined to the semi-arid and arid desert zones of Africa, the Near East and south-west Asia — regions that receive less than 200 millimetres of rain per year. This covers an area of around 16 million square kilometres, comprising approximately 30 countries. During invasions, the desert locust can threaten the livelihoods of one tenth of the world's population.
The current situation is complex and "extremely alarming", according to the Food and Agriculture Organization of the United Nations (FAO). Locust swarms have spread across the Horn of Africa and East Africa, reaching southern Kenya and northern Tanzania, north-east Uganda, south-east South Sudan and north-east the Democratic Republic of the Congo. Despite the control measures put in place, the invasion has already spread to other countries, including Iran, Sudan and Yemen. The worst-affected countries, for now, are Kenya, Ethiopia and Somalia, where there is an unprecedented threat to livelihoods and food security.
The Horn of Africa in particular is facing the worst desert locust crisis in 25 years; the most severe in 70 years for Kenya. An estimated 20.2 million people are facing acute food insecurity. As the growing season approaches, the locust invasion risks pushing this figure even higher. "All the arid and semi-arid regions, where agricultural productivity is low and communities live off subsistence, will be the most vulnerable areas if those communities are attacked," said Sergio Innocente, FAO regional expert on emergency prevention and response in the area of food security, in an interview with LifeGate conducted via a link from Nairobi.
Let us retrace the key events that led to the extreme spread of locust swarms. To do so, we need to go back a few years. In 2018, two cyclones brought heavy rainfall to the Arabian desert and fuelled the reproductive proliferation of locusts. In 2019, locusts reproduced and spread even further; another storm, rare for the region, maintained favourable conditions. Locusts, in fact, proliferate in conditions of abundant vegetation. Furthermore, according to Keith Cressman, entomologist and FAO's leading expert on locust forecasting, the passage of Cyclone Mekunu in 2018 over the "empty quarter", the vast uninhabited desert of the southern Arabian Peninsula, "filled" the spaces between the sand dunes with ephemeral lakes, favouring locust reproduction.
The favourable breeding conditions in the Arabian desert allowed locusts, again according to FAO, to multiply up to eight thousand times. In the autumn months of 2019, the insects pushed from Somalia and Ethiopia into Kenya and Uganda. In Kenya, FAO's locust observation service identified a swarm up to 60 km long and 40 km wide, roughly the size of Luxembourg. It was composed of around 20 billion locusts.
"There have been a couple of climate events that generated particularly favourable conditions for the proliferation of locusts," Innocente explains. "A cyclone off the coast of Oman last June, where there was an initial increase in the locust presence on the Arabian Peninsula. But what was truly a game changer was the cyclone that struck the coast of the Horn of Africa in December. It brought far more moisture to the Horn — so much so that we almost completely lost the dry season at the start of the year. This created even more favourable conditions both for the migration of swarms from the Arabian Peninsula and for the reproduction of those swarms that had already entered East Africa around September. That is where it all started, and then we found ourselves in December and January with a situation that was almost uncontainable, effectively."
What, then, is the relationship between locusts and ecological balance? The conditions favourable to reproduction appear to be precisely the presence of moist sandy soil, the availability of certain "bare" areas for egg-laying and, finally, green vegetation that encourages the development of hoppers.
The hyperactive cyclonic activity of 2018 and 2019 is rather unusual. Across the entire Horn of Africa, rainfall between last October and mid-November was 300 per cent above average, and in Kenya, 400 per cent above average. Overall, the Horn of Africa was struck by eight cyclones in 2019, recording the highest number in a single year since 1976. An analysis by Carbon Brief explains that the unusual wet weather in East Africa is linked to a broader climate system known as the Indian Ocean Dipole (IOD). The dipole influences the climate on both sides of the ocean. When it is in a "neutral" phase, the waters around Indonesia, Papua New Guinea and Australia are warm and winds blow westward.
In this phase, the dipole has a minimal effect on temperatures in the countries surrounding the Indian Ocean. In what is called a "positive" phase, however, this pattern reverses. The westerly winds weaken and, at times, easterly winds form that drag warm waters towards the Arabian Peninsula and the Horn of Africa. This mechanism, in turn, generates cyclones and heavy rainfall in the region. The frequency of cyclones increases during a positive dipole phase, as the additional heat and moisture act as "fuel" for the storms. It is no coincidence that the IOD was in a positive phase both during the June–December 2018 period and throughout 2019, the year in which the dipole reached its most extreme positive level in the past 40 years.
As well as fuelling rainfall in East Africa, the positive dipole played an important role in the dynamics of the bushfires in Australia: this is because the rainfall shifted towards East Africa, leaving Australia in drought conditions. But the unsettling correlation between climate systems does not end there. Climate change could push the dipole towards more frequent positive phases because the western Indian Ocean — near Africa — is warming at a faster rate than the eastern Indian Ocean.
"It is clear to everyone that the past 20 years in East Africa have been years of 'non-normality' — climate events such as drought or abundant rainfall have come with frequencies we are not used to here. Just consider that from the early 2000s to today there has been a climate shock almost every year, whereas before the interval was every 4–5 years," Innocente explains. It is therefore clear that an interaction exists between the unusual cyclonic activity and the locust invasion, compounded by unusually heavy rainfall.
There is a link between climate change and the unprecedented crisis of the locust invasion afflicting Ethiopia and East Africa António Guterres, Secretary-General of the UN
António Guterres, Secretary-General of the United Nations, has also stated: "There is a link between climate change and the unprecedented crisis of the locust invasion afflicting Ethiopia and East Africa. Warmer seas mean more cyclones that generate the ideal breeding ground for locusts. The situation is worsening day by day."
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