In the spring of 2020, a massive swarm of locusts, the largest in seven decades, devastated crops in ten countries in East Africa. This phenomenon caused estimated losses of 8.5 billion dollars, severely affecting a region where 23 million people face severe food insecurity.
The desert locusts (Schistocerca gregaria) are voracious insects, capable of consuming their own weight in food daily. During this biblical plague-like infestation, they managed to devour 160 million kilograms of food per day, enough to feed 800,000 people for a year.
Understanding how these locusts swarm is a challenge that scientists have been researching for decades. Now, a recent study published in the journal Science sheds new light on the collective behavior of these insects.
Vision: the key factor in swarm behavior
The work led by Iain Couzin, a neurobiologist at the Centre for the Advanced Study of Collective Behaviour at the University of Konstanz, reveals that visual signals are essential for locusts to develop group behaviors. While it was previously believed that physical contact between individuals triggered swarms, field experiments and virtual reality have shown that it is visual perception that activates this collective behavior.
“Swarms are not triggered by density, but by the sensory signals they receive,” explains Couzin. This finding changes the way we understand the dynamics of these arthropods and has implications for other animal groups, and even in robotics.
Cognitive processes and collective decisions
According to Jan Ache, a neurobiologist at the University of Würzburg, locusts display two distinct behavioral states: solitary and swarming. This change involves a profound adjustment in their neuronal activity, where the same neurons can cause opposite behaviors, such as repulsion or attraction towards other locusts.
The findings also provide insights into how the brain makes decisions in neural systems. “Neurons compete with each other until a decision on movement is made,” adds Couzin, who compares this dynamic to how humans adopt opinions similar to those of their social environment.
Implications and future applications
The discoveries of this theoretical model not only help understand locust swarms but could also be applied to the study of fish schools, flocks of birds, and even in human crowds. Furthermore, Couzin is already implementing this research in the field of robotics to design collective movements in autonomous vehicles.
While it is still early to draw definitive conclusions, this advancement opens up a new path to predict and manage insect swarms and could have applications in various fields, such as security in large human gatherings and pest control.
How long can desert locusts live?
Desert locusts can live for approximately three months. When a generation has matured, the adults lay eggs that, under suitable conditions, can hatch and form a new generation up to 20 times larger than the previous one.
A swarm covering one km2 can contain up to 80 million adult specimens and has the capacity to consume the same amount of food per day as 35,000 people.
Cover photo: Ben Curtis/AP
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