How Often Do Locusts Swarm?
Locusts are related to grasshoppers and the two insects look similar. Locusts are sometimes solitary insects with lifestyles much like grasshoppers, but locusts have another behavioral phase called the gregarious phase. When environmental conditions produce many green plants and promote breeding, locusts can congregate into thick, mobile, ravenous swarms.
Locust swarms devastate crops and cause major agricultural damage and attendant human misery—famine and starvation. They occur in many parts of the world, but today locusts are most destructive in sustenance farming regions of Africa. The desert locust is notorious. Found in Africa, the Middle East, and Asia, they inhabit some 60 countries and can cover one-fifth of Earth’s land surface. Desert locust plagues may threaten the economic livelihood of one-tenth of the world’s humans.
A desert locust swarm can be 460 square miles (1,200 square kilometers) in size and pack between 40 and 80 million locusts into less than half a square mile (one square kilometer). Each locust can eat its weight in plants each day, so a swarm that large would consume 423 million pounds (192 million kilograms) of plants every day.
To put this in perspective, a swarm the size of New York City would eat as much in one day as the human populations of New York, New Jersey and Pennsylvania combined. Plagues of this size don’t develop overnight, but require several months of optimal breeding and feeding conditions.
Like the individual animals within them, locust swarms are typically in motion and can cover vast distances. In 1954, a swarm flew from northwest Africa to Great Britain. In 1988, another made the lengthy trek from West Africa to the Caribbean.
Although swarms of biblical proportions are less likely in modern times due to pesticide use, six major plagues have occurred in the 1900s. One of these epic plagues persisted for 13 years. Until recently, little was known about why locusts change their behavior when in company – grouping together to indulge in widespread mayhem.
But now, zoologists say they have identified the biological mechanism that causes locusts to swarm. A study by the universities of Oxford, Cambridge and Sydney has found a build-up of serotonin in the nerves of the middle part of the locust’s body controlling its legs and wings causes, within the space of a couple of hours, the solitary locust to turn into its swarming alter-ego.
The finding opens the possibility of stopping the process long before it happens, by blocking the action of serotonin. This could be used to prevent the massive destruction of crops that occurs when locusts swarm – a threat affecting the livelihoods of one-tenth of the world’s population.