Cicadas are a remarkable group of insects known for the dramatic, synchronized nature of their emergence and the extraordinarily loud sound produced by the males. These insects spend the majority of their lives hidden underground, only to appear en masse for a brief period of mating and egg-laying. Their sudden, noisy arrival has historically been interpreted by people as a signal of various changes, ranging from immediate environmental shifts to profound cultural and spiritual concepts. The appearance of cicadas is a biological event that serves as a distinct marker for the passage of time both in nature and in human culture.
The Biological Signal: Marking Seasonal Change
The most direct and scientific sign cicadas offer is the precise timing of seasonal transition, acting as a natural thermometer for the environment. Periodical cicadas, belonging to the genus Magicicada, spend 13 or 17 years developing as nymphs before their synchronized appearance above ground. Their enormous, synchronized emergence is a biological strategy known as predator satiation, ensuring that enough individuals survive to reproduce despite a sudden feast for local wildlife.
The trigger for this mass exodus is tied directly to the earth’s temperature, signaling the end of the cool spring and the onset of summer warmth. Nymphs burrow their way to the surface only after the soil temperature at a depth of about eight inches consistently reaches 64 degrees Fahrenheit. This specific temperature threshold is the final, non-negotiable cue that releases the entire brood from their subterranean existence.
Annual cicadas, sometimes called “dog-day cicadas,” also emerge every year, but their life cycles are staggered. This means some individuals complete their two- to five-year development underground each summer. The overwhelming chorus of the periodical species, however, is a much more dramatic signal because every individual in the local population emerges at once. Their long, prime-numbered life cycles are believed to have evolved to prevent predators with shorter life spans from developing a reliance on them as a consistent food source.
The nymphs manage to track the passing of years underground by sensing the seasonal changes in the xylem fluid they consume from tree roots. This fluid transports water and nutrients, subtly changing its composition as the host tree goes through its annual cycle of leafing out and dropping leaves. This physiological cue acts as a sort of internal calendar, allowing the insects to count the years until their final, simultaneous emergence.
Ecological Indicators of Ecosystem Health
Beyond indicating a seasonal shift, the presence of cicadas offers a report on the health and stability of the local ecosystem. The fact that a massive brood can emerge indicates the land has remained largely undisturbed for over a decade, as the nymphs require stable, uncompacted soil for their long subterranean development. Their existence confirms the presence of mature, healthy deciduous trees, since the nymphs feed exclusively on the roots of these host plants for their entire long lives.
As the nymphs dig their way out and create a dense network of exit tunnels, they perform a significant service known as soil aeration. This natural tillage improves the soil structure, enhances water infiltration, and makes the ground more conducive to root growth for the surrounding vegetation. Cicadas are therefore considered bioindicators, with their abundance suggesting a high degree of soil integrity and minimal recent human disturbance or chemical contamination.
The sudden, enormous biomass of the emerging insects creates a massive, temporary surge in the local food web, providing a high-protein feast for a wide variety of predators. Birds, reptiles, small mammals, and fish temporarily benefit from the abundance, which can lead to a short-term boost in the reproductive success of these predator populations.
When the adult cicadas die after their brief mating period, their corpses rapidly decompose, adding a substantial pulse of nutrients back into the soil. This process acts as a form of natural fertilization, enriching the ground with nitrogen and other compounds essential for plant growth.
Cultural and Symbolic Meanings
The unusual life cycle of the cicada, marked by years of silence followed by sudden, loud emergence and transformation, has led to rich cultural and symbolic interpretations across the globe. In many cultures, the act of shedding the nymphal skin and emerging as a winged adult is a powerful symbol of transformation, renewal, and spiritual rebirth. This metamorphosis is seen as a metaphor for overcoming adversity and achieving a higher state of being.
In Ancient China, the cicada was an emblem of eternal life and immortality, with its sudden appearance from the earth seen as an analogy for the soul’s ascent to a transcendent realm. During the Han Dynasty, jade cicada amulets were ritually placed on the tongue of the deceased before burial. This practice reflected a profound hope that the jade’s purity and the insect’s life cycle would promote resurrection.
For various Native American tribes, the cicada holds a deep significance related to endurance, change, and the passage of time. The Navajo consider them explorers, while the Hopi recognize a Cicada Kachina, a spirit-being associated with the ancestral world. In some tribes, the arrival of the cicadas and their song were interpreted as a sign of impending rain and the promise of abundant crops and fertility.
The distinct sound itself is a significant cultural sign, marking the height of the summer season in many parts of the world. In Japan, the characteristic chorus is the official, auditory start of summer, deeply integrated into the cultural experience of the season. Similarly, in the South of France, the cicada’s persistent song is a sign of good luck, symbolizing a prosperous harvest and crops growing strong under the Mediterranean sun.