Global Plant Protection News

Over the past two years, locusts have ravaged swathes of East Africa. But the cure for the problem may also have dire consequences

THE WEEK STAFF19 NOV 2021

A farmer walking through a swarm of locusts in Meru, Kenya, on 9 February 2021

Yasuyoshi Chiba/AFP via Getty Images

Most of the time, the desert locust, Schistocerca gregaria, is an innocuous grasshopper: a green or brown short-winged insect that lives a solitary life in the deserts of Africa, Arabia and Asia. But in certain conditions – when there’s lots of moisture and vegetation flourishes – these locusts enter a “gregarious phase”, and undergo a remarkable transformation.

• Locusts ravage East Africa’s crops in worst invasion in 25 years
• The Week Unwrapped podcast: Testosterone, vegans and locusts

Their brains change, they turn yellow and black, and their wings grow. Most importantly, they become attracted to each other and start joining together in swarms which can reach a density of 15 million insects per square mile, and travel up to 90 miles in a day. Since late 2019, vast clouds of these locusts have devastated parts of the Horn of Africa, devouring crops and pasture, triggering a huge operation to track and kill them.

Where did the locusts come from?

In 2018, two unusual cyclones – linked to climate change – deposited rain in the remote Empty Quarter of the Arabian peninsula, which led to an 8,000-fold increase in locust numbers there.

In 2019, strong winds blew the growing swarms first into Yemen, then across the Red Sea into Somalia, Ethiopia, Eritrea and Kenya, where their populations were further boosted by a wet autumn, and a cyclone in Somalia – paving the way for a major emergency last year. Billions of the insects swept on, into Uganda, South Sudan and Tanzania, going on to affect a total of 23 countries, from Sudan to Iran to Pakistan.

How big were the plagues?

In Kenya, they were the worst in 70 years. When they arrived in East Africa, witnesses said it was “like an umbrella had covered the sky”. “The first swarms we saw were massive – three or four kilometres wide and a thousand metres deep,” Mark Taylor, a farmer in the Laikipia region of northern Kenya, told The Sunday Times.

A swarm of desert locusts pictured after an aircraft sprayed pesticide in Meru, Kenya

Yasuyoshi Chiba/AFP via Getty Images

When the locusts settled on trees, there were “so many of them that branches broke under the weight”. Locust swarms can vary from less than one square kilometre to several hundred square kilometres. There can be at least 40 million and sometimes as many as 80 million locust adults in each square kilometre. One swarm in northern Kenya was reported to have reached 2,400 square kilometres in size – an area the size of Luxembourg.

How bad was the damage?

Locusts eat their body weight in food every day; a small swarm covering one square kilometre can eat the same amount as 35,000 people. So when they descended on East Africa, vast swathes of vegetation were consumed within minutes. “They attacked everything,” says Mark Taylor. “Fifty-four hectares [133 acres] were destroyed just like that.”