Grasshoppers are common insects found across diverse landscapes, known for their powerful jumping legs and herbivorous diet. Among many species, certain types of grasshoppers can transform into a more destructive form known as locusts. This shift turns a solitary individual into a member of a massive, coordinated group.
Distinguishing Grasshoppers from Locusts
While all locusts are technically a type of grasshopper, not all grasshoppers can become locusts. Locusts belong to a specific group of short-horned grasshoppers within the family Acrididae, possessing the ability to switch between a solitary and a gregarious (swarming) phase. In their solitary phase, these insects behave like typical grasshoppers, living independently and blending into their environment with consistent coloration, such as green or sandy hues. They are shy and avoid other individuals.
In contrast, locusts in their gregarious phase undergo distinct changes in appearance and behavior. They develop stronger wings for long-distance migration, and their coloration changes, becoming more uniform or adopting brighter, warning colors. Behaviorally, solitary grasshoppers are largely nocturnal or crepuscular, relying on camouflage. Gregarious locusts become day-active and are strongly attracted to other locusts, moving in groups. This ability to switch between phases is known as phase polyphenism.
The Transformation Trigger
A primary environmental trigger for this transformation is overcrowding. When grasshoppers are in close proximity, they experience increased physical contact, especially tactile stimulation of their hind legs. This sustained exposure to crowded conditions initiates a series of physiological and behavioral changes.
Other contributing factors can exacerbate this shift. Periods of drought, for instance, can concentrate large numbers of grasshoppers onto dwindling patches of vegetation, intensifying the overcrowding. Conversely, heavy rains after a prolonged dry spell create ideal conditions for egg-laying and abundant food, leading to population explosions and subsequent overcrowding as resources become scarce. These environmental and social cues signal the need for a gregarious survival strategy.
The Metamorphosis
The transformation involves significant biological and behavioral alterations. A key neurochemical involved is serotonin; an increase in the insect’s nervous system initiates the shift from mutual aversion to mutual attraction. This neurochemical change can turn a solitary individual into a gregarious one in as little as two hours.
Physical changes also accompany this shift. Gregarious locusts develop larger flight muscles and a more streamlined body shape, adaptations for sustained, long-distance flight. While solitary locusts have proportionately longer hind legs and stronger jumping ability for short-distance escape, gregarious locusts prioritize flight endurance. Their body color often darkens, sometimes adopting aposematic (warning) coloration, signaling unpalatability to predators.
The Impact of Locust Swarms
The consequences of this transformation lead to the formation of vast, destructive locust swarms. These aggregations can contain millions of individuals and travel long distances, sometimes up to 90 miles a day. Each locust can consume its own body weight in food daily, leading to rapid and widespread devastation of vegetation.
Locust swarms pose a threat to agricultural productivity, destroying crops and pastureland across vast areas. This destruction results in significant economic losses, food insecurity, and can exacerbate poverty in affected regions, particularly where agriculture is a primary source of livelihood. For instance, a single large swarm can consume as much food per day as 35,000 people, jeopardizing the food supply for millions.