Cicadas are intriguing insects, recognized for their distinctive buzzing songs. They spend most of their lives hidden underground, only to emerge in remarkable numbers. Their unique life cycles and the sheer scale of some emergences have long captured human attention, touching upon cultural beliefs and environmental observations.
The Science of Their Emergence
Cicada emergence patterns are governed by precise biological mechanisms, differentiating between annual and periodical species. Annual cicadas, often seen every summer, typically have life cycles ranging from two to five years, with overlapping generations ensuring some adults appear yearly. These species, like the “dog-day cicadas,” do not emerge in the same synchronized, massive numbers as their periodical counterparts. Periodical cicadas exhibit highly synchronized emergence, appearing en masse only every 13 or 17 years. These longer cycles involve nymphs spending nearly their entire lives feeding on xylem fluids from tree roots underground.
The transition from subterranean life to surface emergence is triggered by specific environmental cues. Mature nymphs construct tunnels to the surface, waiting for the soil to reach a critical temperature. Emergence typically occurs when the soil temperature at a depth of about 8 inches consistently reaches approximately 64°F (17.9°C). This temperature signals to the nymphs that conditions are optimal for their final molt and transformation above ground.
Nymphs often emerge on spring evenings. After emerging, they climb onto nearby vegetation, shed their exoskeletons, and transform into winged adults. The adult stage is brief, lasting only about four to six weeks, during which they focus on mating and females lay hundreds of eggs in woody plant stems. The eggs hatch after six to ten weeks, and the newly hatched nymphs drop to the ground, immediately burrowing underground to begin their long developmental period. Scientists hypothesize that periodical cicadas track the passage of years by sensing seasonal changes in the tree sap they consume, acting as an internal clock.
Cicadas as Cultural Symbols
Cicadas have held varied symbolic meanings across diverse cultures and historical periods. Their dramatic emergence from underground and subsequent transformation into winged adults are often interpreted as powerful metaphors for rebirth, resurrection, immortality, and personal transformation. This cycle of shedding an old form to embrace a new one resonates with themes of renewal.
In ancient Greece, cicadas were highly regarded, often associated with music, poetry, and divine inspiration. They were considered sacred to Apollo, the god of music and prophecy, and their singing was seen as a connection to the muses. Athenians wore cicada brooches, symbolizing their connection to song.
Chinese culture also deeply integrates cicada symbolism, representing immortality, rebirth, and protection. Their prolonged underground existence and sudden appearance were seen as analogies for eternal life. Jade cicadas were often placed on the tongues of the deceased, believed to aid in resurrection.
Native American traditions, such as those of the Hopi and Navajo, view cicadas as symbols of life’s constant changes, transformation, and rebirth. Their emergence can also be interpreted as a harbinger of rain and abundant crops. The cicada’s loud and distinctive song is often interpreted as a celebration or a voice finding expression after long periods of dormancy.
Environmental Indicators
Cicadas serve as significant environmental indicators, reflecting the health and stability of ecosystems. Their predictable, large-scale emergences, particularly those of periodical cicadas, suggest an undisturbed environment conducive to their long underground development. Large cicada populations signal a resilient ecosystem, as their life cycle relies on continuous forest cover and suitable soil conditions for many years.
Ecologically, cicadas play several roles. Their mass emergence provides a substantial, temporary food source for a wide array of predators, including birds, small mammals, and reptiles. This sudden abundance can satiate predators, ensuring enough cicadas survive to reproduce, a strategy known as predator satiation.
Beyond their role in the food web, cicadas contribute to soil health. As nymphs tunnel underground, they aerate the soil, improving its structure and water infiltration. When adult cicadas die, their decomposing bodies return substantial amounts of nitrogen and other nutrients to the soil, acting as a natural fertilizer. This nutrient cycling benefits plant growth and overall forest health.
Cicadas also function as a natural clock and a potential indicator of climate change. Their emergence timing is tied to specific soil temperatures and the seasonal cycles of tree sap, which they use to track the years. Warmer springs, a consequence of climate change, can cause cicadas to emerge earlier than historically observed, potentially disrupting their precise internal timing mechanisms.