How a single locust becomes a plague

Vast swarms of desert locusts are tearing through the Horn of Africa and south Asia, devouring crops and threatening food supplies and livelihoods. It's the worst infestation in a quarter of a century. How did it get so bad?

Detailed image of a desert locust

A desert locust like this - a type of grasshopper - usually likes to live a shy, solitary life. It develops from an egg into a young locust - known as a hopper - and then into a flying adult. It's a simple, if unremarkable, existence.

Detailed image of a gregarious desert locust

But every now and then, desert locusts undergo a Jekyll and Hyde transformation. When they get crowded together - such as on diminishing areas of green vegetation - they stop being solitary creatures and become "gregarious" mini-beasts.

In this newly-sociable phase, the insects change colour and form groups that can develop into huge flying swarms of ravenous marauding pests.

Such swarms of locusts can be huge. They can contain up to 10 billion individuals and stretch over hundreds of kilometres. They can cover up to 200km (120 miles) in a day, devastating rural livelihoods in their relentless drive to eat and reproduce.

Even an average swarm can destroy crops sufficient to feed 2,500 people for a year, according to the UN's Food and Agriculture Organisation (FAO).

The last major upsurge - a sharp rise in the number of swarms - in West Africa in 2003-05 cost $2.5bn in harvest losses, according to the UN.

But there were also large and damaging upsurges in the 1930s, 40s and 50s. Some of them spanned multiple regions, reaching the numbers required to be declared a "plague".

Overall, the FAO estimates the desert locust affects the livelihood of one in 10 people on the planet - making it the world's most dangerous migratory pest.

A desert locust like this - a type of grasshopper - usually likes to live a shy, solitary life. It develops from an egg into a young locust - known as a hopper - and then into a flying adult. It's a simple, if unremarkable, existence.

But every now and then, desert locusts undergo a Jekyll and Hyde transformation. When they get crowded together - such as on diminishing areas of green vegetation - they stop being solitary creatures and become "gregarious" mini-beasts.

In this newly-sociable phase, the insects change colour and form groups that can develop into huge flying swarms of ravenous marauding pests.

Such swarms of locusts can be huge. They can contain up to 10 billion individuals and stretch over hundreds of kilometres. They can cover up to 200km (120 miles) in a day, devastating rural livelihoods in their relentless drive to eat and reproduce.

Even an average swarm can destroy crops sufficient to feed 2,500 people for a year, according to the UN's Food and Agriculture Organisation (FAO).

The last major upsurge - a sharp rise in the number of swarms - in West Africa in 2003-05 cost $2.5bn in harvest losses, according to the UN.

But there were also large and damaging upsurges in the 1930s, 40s and 50s. Some of them spanned multiple regions, reaching the numbers required to be declared a "plague".

Overall, the FAO estimates the desert locust affects the livelihood of one in 10 people on the planet - making it the world's most dangerous migratory pest.

Number of countries reporting swarms, 1926-2019
Year Recession Upsurge or decline Plague
20190180
2018000
2017000
2016500
2015200
2014700
20131000
2012900
2011700
2010400
2009500
2008800
20071300
2006100
20050200
20040230
2003500
2002000
2001000
2000200
1999400
1998700
19971200
19961500
19951500
19941300
19932000
1992500
1991000
1990300
19890150
19880026
19871500
19861200
1985200
1984000
1983700
1982500
1981500
1980600
1979040
19780150
1977300
1976900
1975700
19741100
1973700
1972500
1971400
1970700
19690110
19680250
1967700
1966200
1965400
1964600
19630100
19620290
19610290
19600044
19590047
19580041
19570037
19560035
19550043
19540040
19530043
19520027
19510410
19500330
1949900
19481200
19470290
19460360
19450042
19440047
19430043
19420035
19410240
1940060
1939500
1938300
1937600
1936600
1935600
1934090
19330180
19320027
19310035
19300045
19290041
19280034
19270220
1926080
Source: FAO
Note: Recession means locusts are present at low density; upsurge means several locust outbreaks have accelerated through breeding; a plague means widespread and heavy infestations for more than a year; the end of a plague is called a decline.

Swarms are devastating crops in East Africa and Pakistan

The worst swarms of desert locusts in decades are now decimating crops and pasture across the Horn of Africa - an area covering Djibouti, Eritrea, Ethiopia, and Somalia - and beyond, threatening the food security of the entire sub-region.

The ravenous insects are currently spreading through Kenya after wreaking havoc in Somalia and Ethiopia. It is the worst infestation in Kenya for 70 years and the worst in Somalia and Ethiopia for 25.

Somalia has declared a national emergency in response to the crisis. It is the second country to do so after Pakistan, where the insects have ravaged cotton, wheat, maize and other crops in eastern areas.

But it is the Horn of Africa that is of most concern, the FAO says, with the locusts breeding so fast that numbers could grow 500 times by June.

A number of countries are on locust alert

Map showing how locust swarms are infesting the Horn of Africa, both sides of the Red Sea and the India-Pakistan border. Swarms are also moving across Ethiopia and Kenya and could move to other countries. Source: FAO, February 2020

Some swarms crossed the border into Uganda on Sunday the country's authorities said, and the FAO has warned the upsurge could become a regional plague if not tackled.

The pests had already destroyed more than 175,000 acres of farmland in Somalia and Ethiopia by the end of December.

They are eating 1.8m tonnes of vegetation a day across 350 sq km (135 sq miles), the FAO says.

The organisation believes one swarm in Kenya covered an area 40km by 60km (25 miles and 40 miles).

How much can a locust consume?

An adult desert locust can eat its own weight in food every day - about 2g Infographic showing how much a desert locust adult can eat. It consumes about 2g - the equivalent of its own body weight. A swarm of of one sq km can consume the same as 35,000 people Source: FAO

Authorities in the region now fear the locust crisis could lead to a drop in agricultural production, further threatening food suplies in an area already reeling from the effects of floods and drought. More than 20 million people in the region could be affected, the UN says.

"We're most concerned about Kenya and Ethiopia because these are the two areas that have very large swarms," says Keith Cressman, the FAO's senior locust forecasting officer.

"In addition, in Ethiopia, there is breeding going on so there are locusts increasing in number."

Image of Ali Bila Waqo, whose crops have been devastated by locusts

Ali Bila Waqo, a 68-year-old farmer working in north-eastern Kenya, was hopeful of a good grain harvest this season, with recent rainfall ending a long period of drought.

But the locusts have destroyed all his maize and beans.

"They ate most of our grains and what they didn't eat, dried up," he says. "That has hurt us a lot. We saw the food with our eyes but we never even got to enjoy it."

Mr Waqo, who remembers a previous locust infestation in the 1960s, describes how the swarms blacken the skies.

"It gets dark and you can't even see the sun," he says.

Extreme weather has fuelled the crisis

The causes of the current infestation go back to the cyclones and heavy rains of 2018-19.

Desert locusts typically live in the arid areas of about 30 countries between West Africa and India – a region of about 16 million sq km (6.2 million sq miles).

But the wet, favourable conditions two years ago on the southern Arabian Peninsula allowed three generations of locusts to flourish undetected, the UN says.

The upsurge has been developing since 2018

Map showing how the locust swarms developed over a number of seasons and moved from the Arabian Peninsula to the Horn of Africa and the India-Pakistan border Source: FAO, January 2020

By early 2019, the first swarms headed to Yemen, Saudi Arabia and Iran, breeding further before moving to East Africa.

Further swarms formed and by the end of last year had developed in Eritrea, Djibouti and Kenya.

Image of locusts swarming in the Samburu area of Kenya

Swarms are also developing along both sides of the Red Sea, affecting Egypt, Sudan, Saudi Arabia and Yemen, and along the India-Pakistan border - a situation the UN has described as "extremely alarming".

Even though such infestations are notoriously hard to battle because of the wide geographical area affected, the FAO's Mr Cressman believes more could have been done earlier to tackle this particular locust upsurge.

"If there were greater and more successful efforts of control made in some of the key countries, it might have minimised the situation," he said.

People are trying to tackle the huge swarms

With the locust swarms in the Horn of Africa now unprecedented in terms of their size and destructive potential, countries are scrambling to deal with them.

Containment of the outbreak depends on two major factors - monitoring and effective control.

The Desert Locust Information Service, run by the FAO, provides forecasts, early warning and alerts on the timing, scale and location of invasions and breeding.

But once populations reach critical levels, such as in the Horn of Africa, urgent action needs to be taken to reduce locust populations, as well as prevent more swarms from forming and spreading.

How locust swarms are tackled

Infographic showing how locust swarms can be tackled through pesticide sprays devlivered on foot, by aircraft or ground vehicles Source: FAO

"Very large-scale aerial control operations are needed now in Kenya and in Ethiopia - and ideally in Somalia, but this is just not possible due to the security situation," says Mr Cressman.

"As the [locust] populations now are mainly in mature swarms, it would be ideal to hit them hard with aircraft, so that we can reduce the number that could mature and lay eggs."

Although there is ongoing research into more environment-friendly solutions, such as biological pesticides or introducing natural predators, the most commonly used control method is pesticide spray.

Showered onto the pests via hand pumps, land vehicles or aircraft, whole swarms can be targeted and killed with chemicals in a relatively short period of time.

Efforts to combat the invasion in Kenya have intensified with aerial spraying, but controlling such large populations over large, remote areas remains a logistical challenge.

Image of farmer Ali Bila Waqo's destroyed crops

It is especially difficult in countries and regions that have not had to deal with locusts for decades, as there is no infrastructure in place and no collective memory.

"It can cause considerable panic when swarms do come back," says Mr Cressman.

Action taken in Somalia, Ethiopia and Kenya - as well as Pakistan - will now determine what happens next. If the current upsurge crosses more borders and infests more regions, devastating more crops, it could be declared a "plague".

The UN says aerial and ground spraying operations in the region are currently "insufficient" and it has appealed to international donors for $70m (£54m) in emergency aid to help tackle the crisis.

But for Kenyan farmer Ali Bila Waqo and his family, any action now will be too late. The only thing they could do to battle the pests when they descended was to bang on jerrycans and shout.

Yet, he remains philosophical about what has happened.

"It is God's will. This is his army," he says.

Credits

Words and production by Lucy Rodgers, field production by Joe Inwood, design by Zoe Bartholomew and Millie Wachira, development by Becky Rush, Catriona Morrison and Purity Birir. Locust images by Swidbert R Ott and Stephen Rogers and Getty Images. Kenya farming images by the BBC.


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