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Abu Dhabi, UAETuesday 26 March 2019

Locusts explained: why the insects swarm

Rainfall triggers a fundamental change in their behaviour

Swarms of locusts were expected to enter Jordan from Saudi Arabia. AFP
Swarms of locusts were expected to enter Jordan from Saudi Arabia. AFP

While vast swarms of locusts can make dramatic documentary footage, their arrival often heralds huge crop losses for farmers as the insects feed.

Recent weeks have seen their numbers multiply along the coast of Eritrea and Sudan, creating swarms that have travelled into Saudi Arabia and Qatar.

The UAE too has been hit, with a video filmed last month showing countless thousands of the insects swarming in the Al Dhafra region of Abu Dhabi.

The sighting comes a decade after what was probably the Emirates’ worst locust plague in half a century, when swarms devastated much of Al Ain’s date palms.

Desert locusts are typically solitary creatures that avoid one another to reduce competition for food.

But under certain conditions their behaviour changes to create swarms that can be miles long and contain a billion individuals.

Few are more familiar with the causes of this than Dr Steve Rogers, who has researched this “phase change” in laboratories around the world.

He said the reason behind the shift was commonly due to instances of high, sudden rainfall, leading to a rapid growth in vegetation.

With more to eat, population numbers can surge as the insect breeds – but this increase often proves unsustainable.

“What then happens is these rains don't last,” said Dr Rogers, a research associate in the Department of Zoology at the University of Cambridge.

“You end up with a lot of locusts in an area that cannot support them.”

As the locusts feed on the dwindling vegetation, they make physical contact with each other, which causes the switch from being solitary to being highly gregarious, hence the creatures' scientific name, Schistocerca gregaria.

Key to controlling the change is the neurotransmitter serotonin, which is also important in human mood and is associated with feelings of well-being.

In locusts, serotonin levels can increase five-fold when the creatures are “tickled” with a paint brush in the laboratory, which mimics the physical contact they have with one another in the wild.

“It's kind of similar to birds or wildebeest getting together to migrate – because there's safety in numbers,” said Dr Rogers.

“They have to get out of where they are - which can no longer support them - and move to other regions.”

Normally the swarms' worst impact is on regions on the edge of where their numbers multiplied, areas that “can just about sustain” farming.

Fortunately, the application of insecticides can often wipe out their number and prevent the damage to crops.

The physical, behavioural and neurological changes that locusts undergo when they swarm are well understood, thanks to decades of laboratory research.

“The locust is a big, fairly robust species,” said Professor Chris Miall, a professor of motor neuroscience at the University of Birmingham in the UK who has previously carried out research on locusts.

“You can raise it in the lab and do experiments on it - that's why it became a model insect to study.”

Updated: February 19, 2019 03:58 PM

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