The Mormon Cricket (Anabrus simplex) is a large, flightless insect known for massive population outbreaks. Growing up to three inches in length, it is often mistaken for an invasive species due to the sheer scale of its destructive swarms. However, Anabrus simplex is definitively a native pest of the Western United States. The confusion arises from the dramatic, large-scale movements that cause severe damage to agriculture and rangelands.
Native Range and Classification
The Mormon Cricket is endemic to the arid and semi-arid regions of western North America. Its native range extends across the Great Basin and rangelands from southern Canada to states like Utah, Nevada, Idaho, and Oregon. Despite its common name, the Mormon Cricket is not a true cricket but a type of shield-backed katydid, a relative of the long-horned grasshopper. It belongs to the family Tettigoniidae, distinguishable by its long antennae and the shield-like structure behind its head.
A native species evolved within a specific ecosystem, whereas an invasive species is non-native and causes harm. The Mormon Cricket is an integral, cyclical part of the western ecosystem, even if its population reaches pest proportions. Outbreaks are a natural phenomenon, confirming its status as a native organism that exhibits extreme population swings.
The Swarm Cycle and Behavior
The life cycle begins with eggs laid singly in the soil during the summer. They overwinter and typically hatch in the spring after soil temperatures reach around 40°F. Nymphs pass through seven instars over 60 to 90 days before reaching adulthood. While populations exist at low densities for years, a shift occurs when high numbers combine with resource scarcity, often triggered by drought conditions.
This density-dependent pressure causes the insects to transition from a solitary phase to a gregarious, or swarming, phase. The crickets are flightless, possessing only vestigial wings, so the collective movement is a march in dense bands that can contain millions of individuals. These bands constantly move forward, sometimes traveling up to one mile per day and covering 25 to 50 miles over a season.
The primary driver for this relentless migration is a dual need for protein and salt, combined with an impulse to avoid cannibalism. Crickets that slow down or are injured are quickly consumed by those marching behind them. This threat forces the entire band to maintain its forward momentum in search of new vegetation.
Economic and Ecological Damage
The mass migration of these dense bands results in significant damage, justifying the insect’s designation as a severe pest. In agricultural areas, their voracious feeding habits destroy crops such as alfalfa, small grains, and sugarbeets, leading to substantial financial losses. The feeding activities also severely impact rangeland forage, reducing the available food supply for livestock and native wildlife.
Beyond agriculture, the massive numbers of crickets pose a threat to infrastructure and public safety. When swarms cross roadways, the crushed bodies create a slick, greasy sludge that causes traffic hazards and vehicle accidents. Ecologically, the intense, localized feeding strips vegetation, which accelerates soil erosion, disrupts nutrient cycling, and negatively affects water quality in the affected regions.
Controlling Outbreaks
State and federal agencies employ a combination of management strategies to control large-scale population explosions. Physical barriers are utilized to protect specific areas, such as constructing fences or trenches made of galvanized iron sheeting to divert the marching bands. Pits dug alongside these barriers can then trap the diverted insects.
Chemical control is achieved through insecticide baits, which are often mixed with bran and contain active ingredients like carbaryl. These baits are strategically placed in the path of the marching bands to target the crickets with minimal impact on non-target species. Aerial or ground spraying, often using insect growth regulators such as Dimilin, is deployed over large expanses of rangeland to suppress nymph populations early in the season. These efforts sometimes utilize the Reduced Agent and Area Treatments (RAATs) method, which alternates treated and untreated swaths to reduce the overall amount of pesticide applied.