Most cicadas live between two and seventeen years, though nearly all of that time is spent underground as nymphs feeding on root fluids. The loud, winged adults that dominate summer soundscapes typically survive only a few weeks above ground. What separates “annual” from “periodical” cicadas is not whether one lives longer than the other in total, but how their development is timed, and whether their emergence is synchronized with millions of others on a rigid multi-year schedule.
The Underground Majority of a Cicada’s Life
Regardless of species, a cicada spends the vast majority of its existence as a burrowing nymph, slowly growing through a series of molts while attached to tree roots. The nymphs feed on xylem fluid, the dilute, nutrient-poor sap that flows through a plant’s water-conducting tissue. Because xylem is mostly water with trace minerals and amino acids, growth is painfully slow compared to insects that eat leaves or other animals. This nutritional bottleneck is the main reason cicada development takes years rather than months.
Research on several species shows that when nymphs have access to better-nourished host plants, they can shave years off their development. One Japanese species had a median development time of about eight years on native plants, dropping to five years when raised on fertilized potted aloe. A North American species that normally took three years on its native host finished in two on fertilized asparagus. Growth rates also tend to be faster at lower latitudes, where warmer temperatures extend the active feeding season.
1Oxford Academic (Biological Journal of the Linnean Society). Why cicadas (Hemiptera: Cicadidae) develop so slowlyThese findings underscore a point that surprises many people: cicada life cycles are not entirely hardwired by genetics. Environmental conditions shape how long a nymph stays in the ground, even among species famous for their clockwork timing.
Annual Cicadas Are Not Actually One Year Old
The term “annual cicada” is misleading. Species commonly called annual cicadas, like the greenish dog-day cicadas you hear buzzing in midsummer across North America, take two to five years to develop underground. They are called “annual” only because their generations overlap: some adults emerge every single summer, so from a human perspective the species shows up annually. There is no missing year, no silent gap. Some grass-feeding species around the world can mature within a single year, but these are exceptions rather than the rule.
2ScienceDirect. Encyclopedia of Insects – Section: Chapter 46 – CicadasBecause annual cicada populations are not synchronized, their numbers in any given summer are relatively modest. You hear them individually or in loose choruses, not as the deafening wall of sound that periodical cicadas produce. Their ecological strategy is different too: they rely more on camouflage and individual wariness than on the safety-in-numbers approach that defines their periodical cousins.
Periodical Cicadas and the 13- and 17-Year Cycles
Periodical cicadas belong to the genus Magicicada, and they are found only in eastern North America. They are famous for emerging in synchronized mass events on cycles of either 13 or 17 years. An entire regional population, sometimes numbering in the billions, tunnels to the surface within the same few weeks, mates, lays eggs, and dies. Then the forest goes quiet for over a decade.
While any given location sees an emergence just once every 13 or 17 years, different regions operate on different schedules. These regional populations are organized into groups called broods, which are mostly non-overlapping in geography. The broods vary dramatically in size, from enormous populations spanning multiple states to tiny, extremely localized clusters.
3American Entomologist. The Distribution of Periodical Cicada Magicicada Brood I in 2012 with Previously Unreported Disjunct Populations Hemiptera Cicadidae MagicicadaIn practice, because there are multiple broods on staggered schedules, somewhere in eastern North America experiences a periodical cicada emergence in most years. The famous Brood X, one of the largest, last appeared in 2021 across parts of fifteen states. Broods XIX and XIII made headlines in 2024 because their emergence ranges were adjacent, creating an unusually wide area of cicada activity.
Why Prime Numbers
The fact that periodical cicadas have settled on 13- and 17-year cycles, both prime numbers, has fascinated mathematicians and biologists for decades. The leading explanation involves predator avoidance and hybridization. A cycle length that is a prime number is less likely to coincide with the population peaks of predators or parasites that operate on shorter, non-prime cycles. If a predator booms every two, three, or five years, it would sync up with a 12-year cicada far more often than with a 13-year one.
Prime-numbered cycles also reduce the chance that 13-year and 17-year populations will emerge in the same year and interbreed. Because 13 and 17 share no common factors other than one, the two life-cycle types would co-emerge only once every 221 years. Hybridization between the two could produce offspring on intermediate, non-prime cycles that would be more vulnerable, so the prime cycles are self-reinforcing over evolutionary time.
4PubMed Central. Allee effect in the selection for prime-numbered cycles in periodical cicadasHow Long the Adult Phase Actually Lasts
After spending years underground, an adult periodical cicada typically lives above ground for just four to six weeks. Annual cicada adults survive a similar span, though some individuals may last a bit longer depending on conditions. The adult stage is entirely devoted to reproduction. Males call, females choose mates, mating occurs, eggs are deposited in tree twigs, and the adults die. They do not eat solid food as adults; they can drink some plant fluids, but they are essentially running on energy reserves accumulated during years of nymphal feeding.
Research on a related species confirms that calling, the loud buzzing that defines summer, is one of the most energetically costly things a male cicada does. Males that call more frequently and at higher rates are more attractive to females, but this burns through their stored energy faster.
5PubMed Central. The best of both worlds: cicada males change costly signals to achieve mates while females choose a mate based on both calling and courtship songs As adults age, their body mass declines, consistent with the idea that they are essentially capital breeders, spending down a finite energy budget stored from the nymph stage.6PubMed Central. Age-Related Plasticity Integration in Male Cicadas Tettigetta isshikii: Are Adult Cicadas Capital Breeders?
After a female slits small grooves in a twig and deposits her eggs, the eggs hatch in roughly six to ten weeks. The tiny first-instar nymphs drop to the ground, burrow into the soil, find a root, and begin the years-long process of feeding and growing. The cycle starts again.
Stragglers and the Flexibility of “Fixed” Cycles
Periodical cicadas are famous for their strict schedules, but the cycles are not perfectly rigid. Some individuals emerge a year early or a year late, and occasionally groups emerge four years ahead of schedule. These off-cycle individuals are called stragglers.
7PubMed. Competition and Stragglers as Mediators of Developmental Synchrony in Periodical CicadasThe largest straggler events involve four-year accelerations of 17-year cicadas, meaning they emerge after 13 years instead of 17. Researchers have documented these events quantitatively, finding that a four-year early emergence at one site does not necessarily predict a comparable emergence there the following year. At one study site, the density of four-year-early cicadas reached about 1.28 per square meter, which falls within the range of published estimates for normal on-schedule emergences.
8Journal of the Kansas Entomological Society. Multimodal Life-Cycle Variation in 13- and 17-Year Periodical Cicadas (Hemiptera: Cicadidae: Magicicada)Straggler events are more than curiosities. They may be the mechanism by which new broods form over evolutionary time. If a large enough group of stragglers emerges together, they could potentially establish a self-sustaining population on a shifted schedule, eventually becoming a brood in their own right. The four-year offset is particularly interesting because it is the difference between 13 and 17, hinting that life-cycle switching between the two prime cycles may have happened repeatedly throughout Magicicada’s history.
Evolutionary Roots of Periodical Cicadas
Periodical cicadas are not as ancient as their dramatic life cycles might suggest. Genetic studies indicate that the three major Magicicada lineages, known as the Decim, Cassini, and Decula species groups, diverged relatively recently in evolutionary terms. The earliest split among living lineages occurred roughly four million years ago, with the Cassini and Decula groups separating about 2.5 million years ago. The earliest split of a lineage into distinct 13-year and 17-year life cycles happened only about half a million years ago, within the Decim group.
9PubMed Central. Independent divergence of 13- and 17-y life cycles among three periodical cicada lineagesThe evidence points to the 13-year and 17-year cycles evolving independently in each lineage, not once in a shared ancestor. This parallel evolution strengthens the case that strong selective pressures, predator avoidance, hybridization risk, or both, have repeatedly pushed Magicicada populations toward the same two prime-numbered solutions. Paleoclimate shifts during the Pleistocene ice ages likely played a role, pushing populations into refugia where different cycle lengths were favored.
Predator Satiation and Why Billions Emerge at Once
The synchronized mass emergence of periodical cicadas is one of the clearest examples in nature of a strategy called predator satiation. The idea is straightforward: if enough prey appear at once, predators simply cannot eat them all, and the majority survive to reproduce.
Field studies during 13-year cicada emergences found that birds consumed 15 to 40 percent of the cicada population at sites where cicada densities were low. But at sites where densities exceeded about 24,000 individuals per hectare, birds ate only a small fraction. Predators became full within the first days of the emergence and stayed satiated for several weeks. By the time nestlings hatched and adult birds needed to ramp up foraging again, cicada numbers were already declining naturally. Overall, birds consumed only about 15 percent of the total adult cicada population at the study site where activity was greatest.
10Ecology. Emergence of 13‐Yr Periodical Cicadas (Cicadidae: Magicicada): Phenology, Mortality, and Predators SatiationThe earliest individuals to emerge each spring bear the brunt of predation, essentially sacrificing themselves so the main wave can overwhelm predators through sheer numbers.
11PubMed. Red-winged blackbird predation on periodical cicadas (Cicadidae: Magicicada spp.): bird behavior and cicada responsesWhat Triggers Synchronized Emergence
Periodical cicadas spend 13 or 17 years underground, but the decision to emerge on a particular spring night is driven by soil temperature. Nymphs begin tunneling upward when soil temperatures at their depth reach roughly 64°F (about 18°C). The question researchers have puzzled over is how millions of individuals, spread across a landscape with varying soil conditions, microclimates, and depths, manage to emerge within such a narrow window.
Recent work suggests that the nymphs respond to spatially correlated thermal cues, essentially tracking the same regional warming trend from slightly different underground positions. Because spring warming is gradual and spatially coherent over short distances, neighboring nymphs experience similar temperature thresholds at roughly the same time, producing the coordinated mass emergence that defines these species.
12PubMed. How do cicadas emerge together? Thermophysical aspects of their collective decision-makingHow Cicada Emergences Reshape Forest Food Webs
When billions of cicadas appear and then die within weeks, the ecological ripple effects extend far beyond the cicadas themselves. During the 2021 Brood X emergence, researchers found that more than 80 bird species opportunistically switched their diet to include cicadas. This mass diet change pulled birds away from their normal prey, especially caterpillars. With predation pressure suddenly lifted, caterpillar densities roughly doubled, and the amount of leaf tissue caterpillars consumed on host oak trees doubled as well.
13PubMed. Periodical cicadas disrupt trophic dynamics through community-level shifts in avian foragingThe effect is a striking example of how a sudden abundance of one species can rewire an entire food web. Birds that would normally keep caterpillar populations in check are too busy gorging on cicadas to bother with smaller prey. Oak trees, as a result, can take a noticeable hit from the caterpillar boom even as the cicadas themselves are not feeding on leaves.
Below ground, the mass die-off of adult cicadas delivers a pulse of nutrients, particularly nitrogen, to the forest floor. Decomposing cicada carcasses stimulate soil microbial activity and increase plant-available nutrients in the short term. One study found that cicada-derived fertilization strongly increased tree growth in the year of emergence, and the size differences persisted for at least two years afterward.
14PubMed. The effects of pulsed fertilization and chronic herbivory by periodical cicadas on tree growth However, later research found that these nutrient pulses, while measurable in soil chemistry and in populations of soil-dwelling invertebrates, did not consistently translate into improved tree performance across all sites.
15PubMed Central. Acute resource pulses from periodical cicadas propagate to belowground food webs but do not affect tree performanceThe apparent contradiction makes sense when you consider that trees have deep, extensive root systems that buffer them against short-term nutrient spikes. A few weeks of extra nitrogen may boost growth in some conditions but gets diluted in others by the tree’s existing nutrient reserves and competing demands.
The Zombie Fungus
One of the stranger chapters in cicada biology involves Massospora cicadina, a fungal parasite that specifically targets periodical cicadas. The fungus infects nymphs as they emerge from the soil, and within days the rear portion of the infected cicada’s abdomen is replaced by a chalky mass of fungal spores. The infected cicada continues to fly and behave as though healthy, even attempting to mate, which spreads spores to other individuals.
What makes Massospora remarkable is the degree to which it manipulates its host’s behavior. Infected males begin performing wing-flick signals that are normally produced only by sexually receptive females. These fake female signals attract other males, who attempt to mate with the infected individual, picking up spores in the process. Histological examination of infected cicadas confirmed that the fungal masses completely replace the posterior abdominal cavity, destroying reproductive organs, portions of the digestive tract, and fat bodies.
16PubMed Central. A specialized fungal parasite (Massospora cicadina) hijacks the sexual signals of periodical cicadas (Hemiptera: Cicadidae: Magicicada)17PubMed. Histologic findings of Massospora cicadina infection in periodical cicadas (Magicicada septendecim)
The fungus produces two types of spores during different infection stages. Early-stage infections produce conidiospores that spread to other adults in the current emergence. Late-stage infections produce resting spores that fall to the ground and wait in the soil for the next generation, 13 or 17 years later. The fungus has essentially synced its own life cycle to the cicada’s, persisting through more than a decade of dormancy to exploit the next emergence event.
Climate Change and Shifting Emergence Timing
Warming temperatures are beginning to influence cicada emergence patterns. A study of a Japanese cicada species found that higher temperatures from midsummer to early winter in the previous year were associated with earlier emergence the following summer. The mechanism appears to be straightforward: warmer conditions accelerate nymphal growth underground, so the nymphs reach maturity and are ready to emerge sooner.
18Wiley Online Library. Exploring the factors influencing the first singing date of a cicada, Graptopsaltria nigrofuscata: How will it be affected by climate change?For annual cicadas, a gradual shift of a week or two in emergence timing may not be catastrophic, since their generations already overlap. For periodical cicadas, the stakes are higher. Their survival strategy depends on precise synchrony. If warming causes some individuals to develop faster and emerge a year or more early, those stragglers would find themselves alone, without the protection of the mass emergence, and likely face heavy predation. Over time, climate-driven disruptions to synchrony could erode the very mechanism that has made periodical cicadas so successful. Researchers have flagged this as one of the most pressing questions for Magicicada conservation, though nobody yet knows how resilient the system is to gradual warming over the course of a multi-decade cycle.
Telling Them Apart in Your Yard
If you hear cicadas in July or August across most of North America, you are almost certainly hearing annual species. They tend to be larger, with green or brown camouflage coloring, and their song is the classic sustained buzz or drone of a hot afternoon. Periodical cicadas are smaller, with striking black bodies, red eyes, and orange-veined wings. Their songs are higher-pitched and more varied, with different Magicicada species producing distinct call types that researchers can identify by ear.
Periodical cicadas also emerge earlier in the season than most annual species, typically in late April through early June depending on latitude. If you see huge numbers of red-eyed cicadas blanketing tree trunks and sidewalks in May, you are witnessing a periodical brood. If you see a lone green cicada shell clinging to a fence post in August, that is an annual species that quietly completed its multi-year underground development with no fanfare and no synchronized companions. Both spent years underground. Both have only weeks to live as adults. The difference is whether they go through it alone or surrounded by a billion relatives all doing the same thing at the same time.