Mormon crickets are large, flightless crickets native to western North America. Their migratory behavior, forming massive bands, impacts ecosystems and human activities.
Understanding Mormon Crickets
The Mormon cricket (Anabrus simplex) belongs to the Tettigoniidae family. Adult females reach 2 to 3 inches (5 to 7.5 centimeters) in length, while males are somewhat smaller. Their bodies are robust and elongated, covered in a tough exoskeleton that can vary in color from black, brown, red, purple, or green. Though they possess vestigial wings, they rely on walking and occasional hopping for movement.
Mormon crickets inhabit arid and semi-arid regions of western North America, including open grasslands, sagebrush, and desert areas. Their life cycle begins in mid-summer when eggs are deposited below the soil surface, overwintering until spring. Hatching occurs when soil temperatures reach 40°F (4°C), and the nymphs emerge. These nymphs undergo seven developmental stages before reaching adulthood, a process that takes 60 to 90 days.
The Mechanics and Triggers of Migration
Mormon cricket migration is driven by high population density and the search for new resources. When populations become dense, competition for food intensifies, prompting collective movement. Environmental conditions like drought years can exacerbate food scarcity, further triggering these mass migrations. The immediate presence of other crickets also induces locomotion, forming a “forced march” to find food and avoid cannibalism.
These insects form massive bands that can extend for kilometers, sometimes reaching up to 10 kilometers in length and several kilometers wide, with densities of up to 100 individuals per square meter. Their movement is strictly by walking and hopping, due to their short wings. A band can travel 0.5 to 1.25 miles (0.8 to 2 kilometers) in a single day and cover 25 to 50 miles (40 to 80 kilometers) in a season. While they can move at night, migration primarily occurs during the day under clear skies and favorable temperatures, typically between 65°F and 95°F (18°C to 35°C). When two bands encounter each other, they may merge into a larger group or flow through one another while maintaining their respective directions.
Ecological and Economic Impacts
Large-scale Mormon cricket migrations have ecological and economic consequences. Ecologically, their voracious feeding habits lead to widespread defoliation of vegetation, reducing forage for livestock and wildlife. This extensive consumption can result in soil erosion, degraded water quality, and nutrient-depleted soils, altering rangeland and cropland ecosystems. Despite the damage they cause, Mormon crickets also serve as a food source for various predators.
Economically, the impact on agriculture is considerable. Migrating bands can completely destroy cultivated crops such as wheat, barley, alfalfa, and garden vegetables. This damage creates a financial burden for farmers and affected communities. Beyond agricultural losses, Mormon cricket swarms can also affect infrastructure; roads can become slick and hazardous due to crushed crickets. For example, in 2003, Elko County, Nevada, declared a state of emergency due to crickets crawling on hospital walls and making roads slippery.
Mitigation and Management Strategies
Managing Mormon cricket outbreaks involves historical and modern approaches. Historically, physical barriers like fences and trenches were employed to divert or trap migrating bands. Early chemical controls also saw use.
Current integrated pest management (IPM) strategies aim to control populations while minimizing environmental impact. Targeted insecticide applications are a primary method, often involving baits containing active ingredients like carbaryl, a nervous system disruptor, or liquid insecticides such as diflubenzuron, an insect growth regulator. Malathion is another insecticide sometimes used. These applications are often conducted aerially using a Reduced Agent and Area Treatment (RAAT) method, which involves spraying in strips rather than across entire areas to protect non-target species.
Biological controls, though less developed for Mormon crickets compared to other pests, involve enhancing natural predators and parasites. Habitat manipulation, such as tilling vacant lots in late fall to expose eggs to cold temperatures, can also help reduce populations.