Thousands of years after locust swarms became famous in the Christian Bible as one of the plagues that were inflicted upon Egypt; this natural phenomenon continues to bemuse and devastate humans (in equal measure) to this day. Vast swarms that contain billions of locusts stretching several square kilometres periodically affect around 20% of the world’s land surface.
How locust swarms start: the time-old puzzle
For decades, scientists from around the globe had been trying to figure out what turnedharmless grasshoppers (the family from which locusts hail from) from shy solitary insects into brown, crop-devouring clouds of swarming locusts. Finally, after many years, a group of researchers from leading Australian and UK universities cracked the code.
According to the scientists’ publication inScienceMagazine, it was foundthat the build-up of serotonin (a hormone that affects mood in humans) in certain nerves of the locust was what made them turn from timid solitary creatures into the swarming gregarious locusts.
From the beginning
Locust swarms are formed by desert locusts. Before they transform into an all-devouring swarm, desert locusts normally live a solitary life and avoid social contact with other locusts. Because these locusts live in the desert, their populations are usually very smallas there isn’t enough vegetation to support large numbers.
The transition that makes them turn from the solitary state to the gregarious phasehappens after rain falls in the arid areas desert locusts inhabit causing their numbers to explode as there’s more vegetation to sustain larger populations. The subsequent drought forces the solitary locusts to move closer together as vegetation patches shrink.
The enforced mingling of the desert locusts is what triggers the production of the hormone serotonin that causes the usually shy insect to morph into its aggressive alter-ego and become more sociable. Thisphase of the desert locust is born out of desperation and fuelled by hunger as swarms work together to find new pastures.
The now transformed desert locusts in addition to the behavioural change also undergo several physiological changes: their wings lengthen, their hind legs become shorter,and their faces get a more aggressive appearance.
How locust swarms travel
Once the swarm forms, the billions of locusts have no particular course of action or a specific place they’d want to go. They generally rely on wind for transportation. So whether they end up in a barren field, a green field, desert, or even the sea just depends on luck. Ideally, however, they’ll ride the wind to a place where there’s a convergence of winds resulting in rain.
A swarm of locusts can stay aloft for as long as 17 hours at a time and could have a range of up to 5000 Km (or 3,000 miles) in their lifetime if the winds are strong enough.
The Damage caused by locust swarms
A swarm of desert locusts could contain billions of insects with a density of up to 150 million insects per km2. A million locusts weigh approximately 2 tonnes, and 2 tonnes of locusts will eat an equal weight in food in a single day. For perspective, 2 tonnes of food can feed about 20 elephants, 50 camels, or 5,000 people.
With such an appetite, a desert locust plague can wipe out all vegetation wherever it travels to, devouring everything in their way including crops, trees, grass and other plant life.
Locusts are considered a major global pest due to the threat they pose to the agricultural industry and the livelihood of at least a tenth of the people on earth.
Other than greatly impacting food security – an area that is already vulnerable thanks to rapid global population growth – locust swarms also cause environmental degradation as people try to control them using pesticides that sometimes damage the environment.
A lot of research has been done on locust swarms with a lot of positive results. Hopefully, this knowledge can be used in the future to control these plagues and minimise the damage they cause.
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