“Locust” and “grasshopper” are often used interchangeably, causing confusion about whether they refer to the same insect. While both are jumping insects known for consuming vegetation, their relationship is more nuanced than simple synonyms. This article will clarify the biological connection between these insects, detail their distinctions, and explain the remarkable transformation that defines a locust.
Understanding Their Connection
All locusts are a specific type of grasshopper, but not all grasshoppers are locusts. Both belong to the order Orthoptera, which includes insects with “straight wings,” and more specifically, they are part of the family Acrididae, commonly known as short-horned grasshoppers. The key characteristic distinguishing locusts is their capacity to undergo a dramatic behavioral and physical transformation in response to certain environmental conditions, particularly population density.
Only a small number of grasshopper species possess this unique “locust” characteristic. When conditions are not conducive to swarming, these specific grasshopper species behave much like typical, solitary grasshoppers. They maintain low population density and pose no significant agricultural threat.
Key Differences
Distinctions between typical grasshoppers and gregarious locusts are primarily behavioral and morphological. Most grasshoppers are solitary, living independently and rarely interacting beyond reproduction. They tend to remain within a localized habitat, feeding on grasses and leaves.
In contrast, locusts, when triggered, exhibit highly gregarious, swarming behavior, forming massive aggregations that can number in the billions. These swarms can migrate long distances, sometimes covering 5 to 130 kilometers daily, devastating crops. Physically, gregarious locusts develop stronger wings for sustained flight and often change coloration, becoming conspicuously colored with black and yellow or orange patterns, unlike the cryptic green or brown of their solitary counterparts. Their bodies can also become shorter and their muscles larger to support this intense migratory activity.
The Phase Transformation
The shift from solitary grasshopper to gregarious locust is driven by phase polymorphism or density-dependent phenotypic plasticity. This transformation is primarily triggered by increased population density and favorable environmental conditions, such as rainfall that leads to abundant vegetation. As individual grasshoppers are forced into closer contact, physical stimulation, particularly repetitive touching of their hind legs, acts as a potent signal.
This external stimulus initiates internal biological changes, including significant hormonal shifts. An increase in serotonin levels in specific parts of the locust’s nervous system is a key factor in launching the behavioral changes that lead to the gregarious phase. This neurochemical alteration causes the insects to become more mobile and actively seek the company of other locusts, reinforcing the aggregation. The entire process, from initial crowding to behavioral gregarization, can occur rapidly, sometimes within a few hours, though morphological changes develop more gradually.