Grasshopper outbreaks, often involving vast swarms that consume agricultural crops, frequently lead people to question the insects’ origin. These voracious, leaping insects are commonly associated with significant damage, prompting the assumption they must be an introduced, non-native threat. The central question is whether these troublesome species are truly invasive organisms brought from another continent or simply native pests whose populations have exploded under certain environmental conditions. Understanding their ecological classification provides clarity on their role and how they should be managed.
Native Pests Versus Invasive Species
The distinction between a native pest and an invasive species rests entirely on the organism’s origin and the scope of the harm it causes. A native species is one that naturally originated and developed within a specific ecosystem. When a native species experiences a population boom and causes economic damage, such as crop destruction, it is classified as a native pest.
In contrast, an invasive species is formally defined as a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm. Not all non-native species are invasive; many cause no harm. The vast majority of grasshoppers responsible for agricultural losses in the United States are entirely native insects experiencing natural, destructive population cycles.
The term “invasive” cannot correctly be applied to a native organism, even if it is aggressively damaging, because it lacks the necessary non-native origin. The problematic grasshoppers encountered are indigenous insects that have adapted well to the altered landscapes of farming and ranching. Their damage is the result of a population explosion within their native range, not the consequence of a foreign introduction.
Common Grasshopper Species and Their Roles
The insect order Orthoptera is divided into two suborders: Caelifera (short-horned grasshoppers) and Ensifera (long-horned grasshoppers, crickets, and katydids). The short-horned variety includes the pest species and is characterized by antennae much shorter than the body length. North America is home to hundreds of native grasshopper species, but only about 10 to 20 species reach numbers that cause substantial damage.
Most species are benign or beneficial, playing a foundational role as primary consumers and nutrient recyclers. Grasshoppers consume vegetation, and their waste products return nutrients to the soil. They also represent a major food source for many grassland birds, reptiles, and small mammals. The differential grasshopper and the two-striped grasshopper are common native pests that cause localized damage to crops and gardens.
Understanding Outbreaks and Swarming Behavior
The perception of grasshoppers as an overwhelming force often stems from their ability to undergo a dramatic biological change known as phase polymorphism. This mechanism allows a solitary, cryptic grasshopper to transform into a gregarious, migratory locust under certain conditions. The primary trigger for this transformation is density-dependent crowding, where repeated physical contact between individuals stimulates a neurological change.
Once a certain population density is reached, the insects transition to the gregarious phase, changing their color, behavior, and physiology to support mass migration and feeding. Environmental factors facilitate this crowding, often involving drought that concentrates insects onto small patches of vegetation. When subsequent rainfall leads to a population boom, these dense groups are forced into close contact, triggering swarming behavior.
Historically, the native Rocky Mountain Locust caused some of the most devastating insect plagues recorded in North America before its extinction. This species was a native insect whose unique biology allowed it to devastate vast areas when conditions were right. The scale of these outbreaks, which can involve billions of individuals, is rooted entirely in a native species’ natural, density-driven survival strategy.
Managing Grasshopper Populations
Managing grasshoppers requires a multi-faceted approach, especially when dealing with high-density populations. One effective strategy involves cultural control, such as tilling unmanaged, weedy areas in the fall to destroy egg pods laid in the soil. Maintaining a well-irrigated lawn and garden also helps, as grasshoppers often move from dry areas to seek out green food sources.
Protecting individual, high-value plants is possible using physical barriers, such as floating row covers or fine metal screening. For biological control, encouraging natural predators like guinea fowl or chickens can be highly effective, as they actively hunt and consume the insects.
Chemical control is most effective when applied early, targeting the small, less-mobile nymphs in late spring and early summer. Targeted options include baits containing Nosema locustae, a naturally occurring fungus, or granular insecticides applied to perimeter areas. Once grasshoppers reach the adult stage, control becomes much more difficult, requiring repeated applications of approved insecticides.