Desert Locusts have been described as a having a natural ‘Jekyll and Hyde’ – style behavioural change. Going from anti-social locusts to plague like swarms that have been known to affect the livelihoods of 1 in 10 people around the world!
When people think of metamorphosis butterflies are the usual go-to example that people have, a physical change that is easily noticed and measured, what is normally overlooked is the mental change that can occur is species cause behaviours the change so drastically that they are almost a different species. The behavioural changes that a locust goes through has been unsolved until recently when scientists uncovered the underlying biological reasons for how solitary locusts change to migrating swarms. The difference between these two behavioural states is so large that it took entomologists until 1921 to realise that both solitary & swarming locusts are the same species.
These findings could lead to new ways that we prevent future plague like swarms. Whilst it has been common knowledge what the stimuli for this amazing transformation is, the understanding of the changes to the nervous system has remained a mystery. Scientists from both the UK & Australia have identified how an increase in serotonin in the insect’s nervous system is a key factor in initiating the changes to the locust behaviour from anti social to swarming.
Locusts are a member of the grasshopper family, but have the ability to live a solitary or a social state depending on its immediate environment. This ability is not shared with other members of the grasshopper family and such a behavioural change is otherwise unseen in the natural world. The difference between these two behavioural states is so large that it took entomologists until 1921 to realise that both solitary & swarming locusts are the same species.
During a solitary state Locusts have a strong aversion to other insects and spend most of their time foraging in the harsh environments that they reside. When the rains arrive, so does an influx of vegetation allowing for the usually solitary insects population to boom.
Living is deserts; the rain is not sustained for long leaving a large population of locusts now without food, allowing for the remaining population to start residing in smaller areas, meaning more physical contact for the locusts. It is this sustained contact with other individuals that is the stimuli for the change in the solitary locust. This change in behaviour makes the locust actively seek out other individual locusts and become extremely mobile in this effort, with this change in behaviour colouration of the locusts changes, and larger flight muscles are formed to allow for sustained travel. Steve Rogers from Cambridge University emphasises that: "The gregarious phase is a strategy born of desperation and driven by hunger, and swarming is a response to find pastures new." This leads to the question; how can the mere presence of a individual lead to such a intense & sustained behavioural change in another?
The answer is a neurotransmitter; the transmitter serotonin is the fundamental factor in this behavioural change. With new research showing that in the laboratory a solitary locust can be changed to a swarming one in 2 hours by touching their hind legs, mirroring the movement that a locust would experience in a crowded environment. This influx of serotonin in specific parts of the nervous system, in this case the thoracic region, is the catalyst that leads to the behaviour change. This finding was secured when scientists injected locusts with chemicals that block the action of serotonin on receptors then repeated the experiment with no behavioural change occurring in the animals, chemicals that block the production of serotonin also had the same effect. They also gave locusts serotonin, or serotonin mimicking chemicals, and found that locust turned social even without other stimuli.
Serotonin has a pivotal role in human behaviour and interactions, so finding that is has such a major impact on a ‘primitive’ brain, making a normally antisocial insect change into swarms of biblical proportions is revolutionary. With this greater understanding of how this neurotransmitter can change behaviour can help to control future swarms and help to understand behaviours of other animals.
Professor Steve Simpson of Oxford and Sydney Universities said: "No other biological system is understood from nerve cells to populations in such detail or to such effect: locusts offer an exemplar of the how to span molecules to ecosystems - one of the greatest challenges in modern science.