Cicadas, with their distinctive buzzing and synchronized appearances, are a common sight and sound. Their sudden, widespread emergence followed by a rapid die-off often prompts questions about their swift end. This phenomenon is deeply integrated into their biological existence, with their life cycle offering insight into their abrupt demise.
The Cicada Life Cycle
Cicadas undergo a three-stage life cycle: egg, nymph, and adult. Females deposit eggs in slits they create in tree branches. These eggs hatch into tiny nymphs that drop to the ground and burrow into the soil. Underground, nymphs spend years feeding on watery sap, known as xylem, from tree roots.
For most species, the nymphal stage lasts two to five years, while periodical cicadas remain underground for 13 or 17 years. Once mature, nymphs emerge from the soil, typically at night, and undergo a final molt to become winged adults. The adult phase is remarkably brief, lasting only four to six weeks, during which their primary purpose is reproduction.
The Biological Imperative of Death
The adult cicada’s life is a reproductive sprint, following semelparity, where an organism reproduces once and then dies. After years accumulating energy as nymphs, the adult form specializes in a single, intense period of mating and egg-laying. Male cicadas invest significant energy producing loud songs to attract females, who then lay hundreds of eggs in tree branches. This extensive reproductive effort depletes their resources, leaving little capacity for continued survival. The rapid decline and death of adult cicadas after reproduction are a natural, predetermined outcome, signifying the successful continuation of their species.
Factors Contributing to Adult Mortality
Beyond their programmed life cycle, external factors hasten adult cicada death. During mass emergence, cicadas become a readily available food source for numerous predators. Birds, small mammals, reptiles, and cicada killer wasps actively prey on them. Their sheer numbers, a strategy called predator satiation, ensure enough individuals survive to reproduce despite losses.
Environmental stressors also play a role. Harsh weather, such as extreme heat or heavy rainfall, can weaken or kill them. Physical injuries during emergence, flight, or mating further contribute to their decline.
Additionally, pathogens like the parasitic fungus Massospora cicadina infect cicadas. This fungus can replace the cicada’s abdomen with a chalky mass of spores and alter its behavior to facilitate further fungal spread. The intense physical exertion of constant singing, flying, and mating also leads to rapid exhaustion, contributing to their brief adult lives.