Cicadas are insects known for their distinctive, loud buzzing chorus that fills the air. Their sudden appearance in large numbers is a striking natural event, prompting many to wonder about the duration of their presence. These creatures spend most of their lives hidden underground, emerging for a short period before disappearing.
The Brief Adult Lifespan
The adult phase of a cicada’s life is brief, lasting only a few weeks once they emerge from underground. The time spent above ground as a winged adult is typically short, lasting from 20 days to a month. This brief existence is dedicated entirely to reproduction.
Cicadas are broadly categorized into annual and periodical types; both have a short adult stage. Annual cicadas, despite their name, spend years underground, generally two to five years, but some adults emerge every summer, giving an annual impression. Periodical cicadas, found in eastern North America, are known for their synchronized mass emergences every 13 or 17 years, with adult lives lasting only a few weeks. For both types, the adult cicada’s primary purpose is to mate and lay eggs.
Factors Influencing Their Disappearance
The disappearance of adult cicadas is a natural and inevitable part of their life cycle, driven primarily by the completion of their reproductive imperative. Once males have attracted females with their loud songs and mating has occurred, the females then lay their eggs. This egg-laying process, where females deposit eggs into slits cut into tree branches, signals the near end of the adult cicada’s life.
Environmental factors also contribute to their eventual decline. Emergence from the soil is often triggered by specific cues, such as the ground temperature reaching around 64 degrees Fahrenheit (18 degrees Celsius) at a depth of eight inches. After this initial emergence and the subsequent mating period, cooler weather as the season progresses can accelerate their natural decline. While their sheer numbers offer some protection against predators through a strategy known as “predator satiation,” where there are simply too many for all to be eaten, predation by birds, small mammals, and other insects still contributes to their population reduction.
After the Buzz: What Remains
Once the adult cicadas have completed their short lives, the landscape begins to quiet down as their buzzing chorus fades. Their bodies, having served their purpose, fall to the ground. These deceased insects contribute valuable nutrients back into the ecosystem, as their decomposition enriches the soil, providing a boost of nitrogen and other elements to plants and trees.
The next generation of cicadas is already underway, though unseen. The eggs laid by the females in tree branches typically hatch within six to ten weeks. Upon hatching, the tiny, ant-sized nymphs drop to the ground and immediately begin burrowing into the soil. There, they will spend the next several years, or even more than a decade for periodical species, feeding on sap from tree roots and developing, patiently awaiting their own time to emerge and restart the cycle.