Cicadas, known for their distinctive buzzing chorus, are a temporary but prominent feature of the summer landscape. Their arrival often prompts questions about their duration and when their sounds will subside. Understanding their unique life cycle provides clarity on their temporary stay.
Understanding Cicada Emergence
Cicadas are broadly categorized into two types: annual and periodical. Annual cicadas, such as the common “dog-day cicada,” emerge every summer. While individual annual cicadas spend two to five years underground as nymphs, their unsynchronized emergences mean some adults appear each year. This contrasts with periodical cicadas, known for their synchronized mass emergences after extended periods underground.
Periodical cicadas spend 13 or 17 years as nymphs burrowed beneath the soil, feeding on xylem fluids from tree roots. They emerge in large numbers when soil temperature reaches approximately 64 degrees Fahrenheit (18 degrees Celsius) at a depth of 8 inches, typically between late April and early June. Once above ground, their adult lifespan is brief, lasting only about four to six weeks, primarily dedicated to reproduction.
Factors Signaling Their Departure
The primary reason for the disappearance of adult cicadas is the completion of their reproductive cycle. After emerging, their main purpose is to mate and lay eggs. Male cicadas produce loud songs to attract females. After mating, females use an ovipositor to lay eggs in the twigs of woody plants, a process that typically takes several weeks.
Once adult cicadas have fulfilled their reproductive tasks, they die. Their bodies may be seen on the ground or clinging to vegetation. For periodical cicadas, the entire adult population of a brood dies off within about two months of their initial emergence. For annual cicadas, their active adult period concludes as temperatures decline towards the end of summer.
The Aftermath and Next Generation
After adult cicadas die, their presence leaves noticeable signs. Empty nymphal exoskeletons remain attached to trees, and deceased adult bodies contribute organic matter to the soil. The eggs laid by female cicadas in tree branches will hatch six to eight weeks later.
Newly hatched cicadas, known as nymphs, are tiny and ant-like. Upon hatching, they drop to the ground and burrow into the soil. Once underground, they seek tree roots to feed on xylem fluid, initiating their long subterranean developmental phase. For periodical cicadas, this journey spans another 13 or 17 years before they emerge to repeat the cycle.