Mormon crickets are distinctive insects known for their large aggregations, often forming vast swarms that traverse landscapes. These fascinating creatures, despite their common name, are not true crickets. Their unique biology and migratory habits have drawn considerable attention, particularly in western North America. Understanding their life history helps clarify their impact on ecosystems and agricultural areas.
What Are Mormon Crickets?
Mormon crickets (Anabrus simplex) are large, flightless long-horned orthopterans native to western North America. Despite their common name, they are shield-backed katydids, belonging to the family Tettigoniidae, not true crickets. These insects can reach 8 centimeters (3 inches) in length and display varied coloration, including black, brown, red, purple, or green. They have robust bodies with a tough exoskeleton and long, filamentous antennae that often exceed their body length.
Though they possess vestigial wings, these are not functional for flight; Mormon crickets move primarily by crawling and hopping. They are found in arid and semi-arid regions, inhabiting open grasslands, sagebrush rangelands, and desert environments. Their presence is notable across states like Idaho, Nevada, and Utah, where they thrive in dry conditions.
The Mormon Cricket Life Cycle
The Mormon cricket life cycle begins with the egg stage. Females lay individual eggs in the soil during late summer or early fall, typically up to ¾ inches deep. These eggs then undergo a period of dormancy, overwintering in the ground. Hatching occurs in early spring once soil temperatures reach approximately 40°F (4°C), though some eggs can remain dormant and hatch up to five years later, especially at higher altitudes. Each female can lay 85 to 180 eggs in a season.
Following hatching, the insects enter the nymph stage, passing through seven distinct growth phases, known as instars. This developmental period spans 60 to 90 days, influenced by environmental factors like temperature. Young nymphs often appear black with a white stripe, while older nymphs exhibit a wider range of colors. During this stage, Mormon crickets form large, moving bands.
The final molt marks their transition into the adult stage, where they achieve reproductive maturity within 10 to 14 days. Adult males attract females with a calling song. During mating, the male transfers a large spermatophore to the female, which can constitute up to 27% of his body weight. This spermatophore provides both sperm for fertilization and nutritional support. After mating and egg-laying, the adult phase concludes, completing the annual generation.
How Long Do They Live?
The adult lifespan of a Mormon cricket lasts about 8 to 10 weeks after reaching maturity. This adult phase is dedicated to mating and egg-laying. Their most active period occurs during late spring and summer, aligning with favorable conditions for foraging and reproduction.
While the adult stage is relatively short, the overall lifespan, from egg to adult death, can extend over several months. This includes the long overwintering period of eggs, which may last one to five years in certain conditions before hatching. Nymph development then takes another 60 to 90 days. Thus, the entire life history can span a significant portion of a calendar year, or even multiple years for eggs in prolonged diapause.
Factors Influencing Lifespan
Several factors influence the longevity of Mormon crickets. Temperature and precipitation play significant roles; extreme heat or cold can limit survival, while adequate moisture supports their vegetation. Drought conditions can encourage population outbreaks, but prolonged lack of food and water shortens individual lifespans. Conversely, multiple days of wet and cold weather in early spring can lead to high nymph mortality.
Food availability directly impacts survival and growth. Mormon crickets are omnivorous, consuming over 400 plant species, but prefer forbs and grasses. When plant resources are scarce, they may resort to consuming carrion or engaging in cannibalism, eating injured or dead crickets. This opportunistic feeding behavior helps them survive challenging conditions, though it can also reflect resource scarcity that impacts their health and longevity.
Natural predators also pressure Mormon cricket populations. Birds like California gulls and crows, as well as rodents and coyotes, prey on these insects. Certain parasites, such as the horsehair worm Gordius robustus and the parasitic wasp Ooencyrtus anabrivorus, can also infect them. However, due to their migratory habits and large population fluctuations, no single predator specializes exclusively on Mormon crickets.
Human control efforts also affect their lifespan. Pesticides, such as carbaryl, are used to reduce their numbers, and the insect growth regulator Dimilin has been applied in some areas. Physical barriers, like trenches or fences, can limit their movement and access to food sources, indirectly impacting survival.