Why do locusts swarm?

The [wiki]coronavirus pandemic[/wiki] is not the only challenge East Africa has faced in 2020. Earlier this year the region was hit by a local invasion of locusts that damaged crops. Now another wave is causing more destruction.  According to the United Nations (UN), the food supply of 23 million people is at risk.

 

Most of the time desert locusts are solitary and fly only at night, but right now millions are swarming over East Africa. How can one species change its behaviour so much?

 

ONE SPECIES, TWO PERSONALITIES:

 

Desert locusts can have two very different personalities. These are so different that in the past they were thought to be two different species. Most of the time they are light green, solitary and active at night. In certain conditions however, they begin reproducing rapidly. They become stronger, more motile and start to seek each other out. They even change colour, from green to pink, then black, then bright yellow.  In this state, massive swarms can form that cover up to 460 square miles. A swarm this big can contain up to 80 million locusts and eat 423 million pounds of plants a day.

 

WHEN DOES THIS CHANGE OCCUR?

 

Certain environmental conditions make swarms possible. A rainy period allows locust populations to grow quickly as lots of food is available. If rains are followed by drought, the land becomes dry and less grass grows. This forces locust populations into smaller spaces and soon a density threshold is reached. At this point, personality and appearance changes occur and swarms start.

 

HOW DOES THE LOCUST CHANGE PERSONALITY?

 

In 2009, scientists discovered that changes in a brain chemical was responsible. This chemical is called serotonin, and is also found in human brains. Increasing serotonin is the first step that leads to changes in behaviour and appearance.

 

The scientists proved their theory by doing lots of tests. When locusts were injected with drugs that stopped serotonin working, they didn’t become sociable. Even after contact with many other locusts they remained solitary. The opposite was true when solitary locusts were injected with serotonin. This time, they changed form and behaviour even when alone.

 

WHY IS THIS IMPORTANT?

 

These swarms are a huge threat to people’s livelihoods. If we understand what causes locusts to gather, hopefully swarms can be prevented in the future. It will also allow better prediction of when they might occur and so better preparation.

GEORGINA MILES

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