The transformation of a grasshopper into a locust is a biological event where a single species exists in two different forms. This phenomenon, known as phase polyphenism, involves profound biological changes driven by specific environmental cues. Not all grasshopper species can become locusts; fewer than 20 species worldwide possess this capacity for transformation.
Grasshopper Versus Locust
Grasshoppers live solitary lives, blending into their surroundings with cryptic coloration. They are mostly sedentary, moving primarily to feed or when threatened. In contrast, locusts represent a gregarious, swarming phase of certain grasshopper species.
Locusts undergo changes in appearance and behavior. They develop darker, more contrasting colors like black and yellow or orange. Their bodies become larger with stronger wings, adapted for sustained, long-distance flight. While grasshoppers come together mainly for reproduction, locusts are highly social, forming dense, cohesive groups.
The Environmental Trigger
The transformation of a solitary grasshopper into a gregarious locust is primarily initiated by environmental conditions that lead to increased population density. This often occurs following periods of drought when abundant rainfall causes vegetation to flourish, allowing grasshopper populations to boom. As food resources become scarce and large numbers of insects are funneled into shrinking patches of vegetation, they are forced into close physical contact.
The repeated physical contact among individuals, particularly the tactile stimulation of their hind legs, acts as a trigger for this phase change. This crowding, whether through sight, smell, or touch, signals to the grasshopper that its environment is becoming densely populated.
Internal Transformation
Once environmental triggers are met, biological and physiological changes begin within the insect. Increased physical contact, such as the frequent touching of hind legs, leads to a rapid increase in serotonin levels within the insect’s nervous system. This neurochemical surge is a direct link between external stimuli and internal shifts. Serotonin acts as a neuromodulator, influencing the locust’s behavior and initiating the move from solitary to gregarious tendencies.
This internal shift drives physical alterations. Solitary grasshoppers develop the black and yellow or orange coloration of gregarious locusts. Their muscles, particularly those used for flight, strengthen, and their body shape may change, with shorter front legs and longer hind legs. These morphological and physiological adaptations prepare the insect for a migratory lifestyle, allowing it to tolerate and seek out the company of other locusts.
The Swarming Life
Once fully transformed, locusts exhibit characteristic swarming behavior, a collective movement that distinguishes them from their solitary grasshopper phase. These swarms, which can consist of billions of individuals and span vast areas, move together, often covering hundreds of kilometers per day. Their synchronized movement is driven by individual locusts reacting to their nearest neighbors, creating a robust collective motion.
Locust swarms are voracious, capable of consuming their body weight in vegetation daily and devastating agricultural landscapes. The purpose of this swarming is often to find new food sources when local resources are depleted. The coordinated migration and feeding patterns of these immense groups have historically posed significant threats to food security across continents.