Cicadas are a distinctive group of insects recognized for the loud, often shrill sounds produced by the males. Found globally, they are best known for their unique life cycles. A common misunderstanding suggests cicadas “hibernate” for many years, but this is inaccurate. Instead, they undergo an active, lengthy developmental phase as nymphs living underground. They spend nearly their entire lives in this immature stage before emerging as winged adults for a comparatively brief period.
Life Beneath the Surface
Once cicada eggs hatch, the tiny nymphs drop to the ground and immediately burrow into the soil. Here, they actively feed on xylem fluid from tree roots. This fluid, though not rich in nutrients, provides the necessary sustenance for their growth and development over several years. As they grow, the nymphs undergo multiple molts, shedding their exoskeletons. Most cicada nymphs typically reside within two feet of the surface, though some can be found deeper. This subterranean existence is a period of continuous activity and growth, not a state of dormancy.
Periodical and Annual Cycles
The duration of a cicada’s underground life varies significantly by species, falling into two main categories: annual and periodical. Annual cicadas typically have life cycles ranging from two to five years, sometimes longer. Adults of these species emerge every summer because their broods are not synchronized, meaning different individuals complete their development each year. In contrast, periodical cicadas are distinguished by their highly synchronized emergences, appearing only every 13 or 17 years.
Seven species of periodical cicadas exist: three follow 17-year cycles and four follow 13-year cycles. These long, prime-numbered cycles are an evolutionary strategy that helps them avoid predators. Notable 17-year broods include Brood X (Great Eastern Brood) and Brood XIII (Northern Illinois Brood). Brood XIX is a significant 13-year brood (Great Southern Brood).
Triggers for Emergence
After years of development underground, cicada nymphs are prompted to emerge by specific environmental cues, primarily soil temperature. Nymphs typically begin their ascent when the soil at about 8 inches reaches approximately 64 degrees Fahrenheit. They construct tunnels to the surface before emerging. This emergence usually occurs on a spring evening.
A warm rain can also contribute to triggering emergence, as it helps to warm the soil. The emergence process can take about two weeks.
Life Above Ground
Once cicada nymphs reach the surface, they climb onto vertical structures for their final molt. They shed their nymphal exoskeletons and emerge as winged adults. Adult cicadas reproduce. Male cicadas produce loud calls to attract mates.
After mating, female cicadas lay their eggs in slits they create in plant twigs. Each female can lay hundreds of eggs. Adult cicadas live for only a few weeks before they die, completing their life cycle.