The widespread appearance of insects is primarily due to the emergence of periodical cicadas, species known for their synchronized, massive arrival. These insects, belonging to the genus Magicicada, spend the vast majority of their lives feeding on tree roots beneath the soil surface. Their noticeable presence—the distinctive, loud chorusing—is a direct result of their brief transition to adulthood, a phase dedicated entirely to reproduction. Understanding when this intense, noisy period will conclude depends on the insects’ biological clock and local environmental variables.
The Adult Cicada Timeline
The visible and audible phase of a periodical cicada emergence is surprisingly short, generally lasting between four and six weeks in any specific location. This brief period represents the culmination of a 13-year or 17-year lifecycle spent as nymphs beneath the earth. Once they molt into their winged adult form, the insects’ only remaining function is to mate and lay eggs before their natural death.
The perception of when they are “gone” is complicated by the difference between annual and periodical species. Annual cicadas, sometimes called “dog-day” cicadas, appear every summer, but their staggered emergence never reaches the overwhelming numbers that cause widespread attention. Periodical cicadas, conversely, emerge in near-simultaneous swarms, creating the deafening sound that defines the event.
The collective presence does not vanish overnight but slowly tapers off as individuals complete their reproductive tasks. The “end date” for an emergence is effectively the point at which the last groups of adults in a region have finished their mating cycle and died. This staggered, localized completion accounts for the variation in the end of the event.
Factors Determining the Emergence End Date
The timeline for the beginning and end of a local emergence is heavily influenced by temperature, which serves as the biological cue for the insects to leave the soil. Nymphs typically begin to tunnel out of the ground once the soil temperature at a depth of about 7 to 8 inches reaches approximately 64 degrees Fahrenheit. If a region experiences an early spring with consistently warm temperatures, the emergence will begin sooner and, consequently, end earlier.
Conversely, areas that experience a cooler spring or late-season cold snaps will see a delayed start to the emergence, pushing the entire timeline back. Geographic location dictates this thermal schedule, meaning southern regions and lower-elevation areas generally witness the end of the event before northern or higher-elevation spots. This is why a single calendar date for the end of the emergence is impossible to provide.
The specific “Brood” involved also plays a role in the precise timing and geographic footprint of the event. Periodical cicadas are categorized into over a dozen broods, each emerging in a specific year and location based on their 13- or 17-year cycle. For the most accurate local estimate, residents must check entomological reports specific to the Brood currently active in their area, as these account for local microclimates and specific emergence patterns.
What Happens After Cicadas Die
The disappearance of the loud adult population is the first step in the cycle’s completion, which is immediately followed by the subterranean return of the next generation. Before the adults die, the females use a specialized organ called an ovipositor to cut small slits into the bark of young tree branches where they deposit their eggs. A single female can lay hundreds of eggs across many different branches during her short adult lifespan.
The adult insects then die, and their bodies fall to the ground. These deceased insects are quickly broken down by natural processes, returning nitrogen and other valuable nutrients to the soil. This natural fertilization helps nourish the trees that will host the next generation of nymphs.
Approximately six to eight weeks after the eggs are laid, the tiny, rice-sized nymphs hatch and drop from the tree branches to the ground below. They immediately burrow into the earth, where they find tree roots and begin feeding on the xylem fluid. These young nymphs remain hidden underground for the next 13 or 17 years until their own synchronized emergence decades later.