Locusts are a type of insect known for their dramatic swarming behavior, which can have a significant impact on landscapes and human populations. These insects possess a unique capacity to become a formidable collective force. Understanding their nature and life cycle reveals the mechanisms behind these large-scale phenomena.
Defining Locusts: More Than Just Grasshoppers
Locusts are specific species of short-horned grasshoppers (family Acrididae) that can undergo a dramatic transformation, rather than a distinct taxonomic group. Most grasshoppers live solitary lives, blending into their environment and posing little threat. Locusts, however, can switch between two distinct behavioral states: a solitary phase and a gregarious phase. This dual nature, known as phenotypic plasticity, means their physical characteristics and behavior can change significantly based on population density, even though their genes remain the same.
In their solitary phase, locusts resemble typical grasshoppers, often camouflaged with green or brown coloration. They are generally shy, avoid other locusts, and are less active. When environmental conditions lead to increased population density, they transition into the gregarious phase. In this swarming state, their appearance changes; they can develop more vibrant black, yellow, or orange patterns and their wings may become longer and stronger, better suited for long-distance flight.
The Life Cycle and Phases of Locusts
The life cycle of a locust involves incomplete metamorphosis, progressing through egg, nymph, and adult stages. Female locusts typically lay 20 to 100 eggs in pods, several centimeters deep in moist, sandy soil. A frothy secretion protects these eggs and maintains hydration. After 10 days to two weeks, eggs hatch into wingless nymphs, also known as hoppers.
Nymphs develop through several sub-stages (instars), shedding their exoskeleton five times as they grow. They primarily hop and feed voraciously during this period. The transformation into the gregarious phase is often triggered by specific environmental conditions, such as a period of drought followed by heavy rainfall. This sequence leads to abundant vegetation, allowing locust populations to breed rapidly and increase in density.
As numbers swell and contact increases, physical stimuli like touch, visual, and olfactory cues initiate the phase shift. Crowding triggers rapid behavioral changes within hours, including increased activity and mutual attraction, rather than repulsion. Physiological changes, like increased serotonin, also contribute to this shift. Over several generations, these changes become more pronounced, leading to the formation of cohesive marching bands of hoppers and eventually flying swarms of adults.
The Devastating Impact of Swarms
Locust swarms represent a significant threat to agriculture and food security due to their sheer numbers and voracious appetites. A single square kilometer of a swarm can contain between 40 million and 80 million adult locusts. These swarms are highly mobile, flying with the wind at speeds of 16 to 19 kilometers per hour, covering 5 to over 130 kilometers daily. Some swarms have been observed traveling thousands of kilometers, such as one that crossed 5,000 kilometers from West Africa to the Caribbean in about ten days.
The destructive capacity of these swarms is immense. An adult locust consumes roughly its own weight in fresh vegetation daily (about two grams). Consequently, a swarm spanning just one square kilometer can eat the same amount of food in a single day as about 35,000 people. They feed on nearly all types of green vegetation, including crops, pastureland, and fodder. This leads to widespread destruction of agricultural yields, threatening farmer livelihoods and food supplies.
The consequences extend beyond immediate crop damage, contributing to broader issues of food insecurity and substantial economic losses. Recent outbreaks have placed millions of people at risk of starvation, particularly in areas already vulnerable to drought, conflict, and high food prices. For example, a major outbreak in East Africa and Yemen was projected to cause losses amounting to as much as $8.5 billion.