Most cicada species spend between two and five years underground, while the famous periodical cicadas of eastern North America live below the surface for either 13 or 17 years before emerging as adults. None of them are hibernating. Underground cicada nymphs are awake, feeding, growing, and molting through multiple developmental stages for the entire duration of their subterranean lives. The distinction matters because it shapes how we understand these insects and, in the case of periodical cicadas, one of the longest and most precisely timed developmental periods of any insect on Earth.
What Cicadas Are Actually Doing Underground
When people hear that an insect spends over a decade below ground, the natural assumption is that it must be in some kind of dormant state, waiting out the years the way a bear sleeps through winter. Cicada nymphs do nothing of the sort. From the moment they hatch from eggs laid in tree branches and drop to the soil, they burrow down, find a root, and start feeding. They stay active for the entirety of their underground lives, passing through five nymphal stages, each separated by a molt in which they shed their exoskeleton and grow larger.
Nymphs are built for digging. Their front legs are thick and shovel-like, adapted for excavating soil. Studies of burrowing behavior show that nymphs construct air-filled cells in the soil, typically a few centimeters long, through a methodical process: they excavate sediment in front, roll it into a ball, flip around, and push it against the back wall of the chamber.
1PALAIOS. Traces and burrowing behaviors of the cicada nymph Cicadetta calliope: Neoichnology and paleoecological significance of extant soil-dwelling insectsThese aren’t permanent chambers. As nymphs grow and need to relocate to new feeding sites on tree roots, they dig new tunnels. Some tropical species take this further: the nymph of one Amazonian cicada builds a clay turret, 20 to 40 centimeters tall, above the opening of its vertical shaft during its final year underground, apparently to regulate temperature and humidity inside the burrow. The nymph actively maintains, repairs, and rebuilds this structure as needed.
2Ecosystem and Biodiversity of Amazonia. The Nymph Architect of the Cicada Guyalna chlorogena: Behaviours and EcosystemFeeding on Almost Nothing
The reason cicadas need so many years to develop comes down to diet. Nymphs feed exclusively on xylem fluid, the watery sap that moves upward through a tree’s roots and trunk. Xylem is the least nutritious plant fluid available. Unlike phloem sap, which carries sugars and is relatively rich in calories, xylem is extremely dilute, consisting mostly of water with trace amounts of minerals and amino acids. Histological studies of tree roots where periodical cicada nymphs had been feeding confirmed that their mouthparts were inserted into xylem vessels, not phloem cells, throughout all developmental stages.
3Ecological Entomology. Xylem feeding by periodical cicada nymphs on tree rootsLiving on such a dilute food source means growth is extremely slow. To compensate for the nutritional poverty of xylem sap, cicadas rely on bacterial partners living inside their bodies. Many cicadas host two bacterial endosymbionts that produce essential amino acids the insect cannot get from its diet alone.
4Genome Biology and Evolution. No Transcriptional Compensation for Extreme Gene Dosage Imbalance in Fragmented Bacterial Endosymbionts of CicadasEven with this microbial assistance, xylem feeding is a fundamentally limiting way to grow, and it is likely the single biggest reason cicada development takes so much longer than that of other large insects. Researchers who first examined this feeding strategy noted that the habit of feeding on such dilute fluid may explain why periodical cicada nymphs require 13 or 17 years to reach adulthood.
3Ecological Entomology. Xylem feeding by periodical cicada nymphs on tree rootsHow a Cicada Counts to Seventeen
One of the most striking things about periodical cicadas is their precision. Billions of individuals across large geographic areas manage to emerge in the same year, on nearly the same dates, after spending exactly 13 or 17 years underground. That level of synchrony demands an internal timekeeping system, and for decades the mechanism was a mystery. A clever experiment resolved it: researchers manipulated the seasonal cycles of the trees that nymphs were feeding on, essentially giving the trees an extra “year” of growth signals in a compressed timeframe. The nymphs responded by emerging a year early, proving they track time by counting seasonal changes in their host tree rather than measuring the passage of real time or accumulating heat.
5Ecology Letters. How 17‐year cicadas keep track of timeTrees go through a predictable annual rhythm: sap flow increases in spring, peaks in summer, and drops in fall and winter. The chemical composition and pressure of xylem sap fluctuate with the seasons. Nymphs appear to sense these yearly pulses and use them as tick marks on an internal calendar. The working hypothesis for periodical cicadas is that they operate on a four-year internal clock: at developmental “gates” spaced four years apart, a nymph evaluates whether it has reached a critical body weight for metamorphosis. If it has, it prepares to emerge the following spring. If not, it waits for the next gate.
6Ecological Research. Life‐cycle control of 13‐ and 17‐year periodical cicadas: A hypothesis and its implication in the evolutionary processField tests of this “four-year gate” idea have found supporting evidence. When researchers examined nymphs of different ages in autumn, they found that nearly all 16-year-old nymphs had already undergone the eye-color change from white to red that signals their decision to emerge, and their body weights were large enough to have exceeded the critical threshold. A small but real fraction of 12-year-old nymphs had also made the decision to emerge early, consistent with hitting the weight threshold at the 12-year gate instead of the 16-year one.
7PubMed Central. When and how do 17-year periodical cicada nymphs decide to emerge? A field test of the 4-year-gate hypothesisWhy Prime Numbers
It is no coincidence that the two periodical cicada life cycles, 13 and 17 years, are both prime numbers. This pattern has fascinated mathematicians and biologists for over a century, and the leading explanation involves the avoidance of hybridization. Seven species of periodical cicada exist in eastern North America, divided into three species groups. Within each group, there is typically a 13-year species and a 17-year species.
8PubMed Central. Independent divergence of 13- and 17-y life cycles among three periodical cicada lineagesPrime-numbered cycles minimize the frequency with which different broods emerge at the same time. A 12-year cicada and a 15-year cicada would overlap every 60 years, but a 12-year and a 14-year cicada would overlap every 84 years, and so on. With prime numbers like 13 and 17, the overlap interval is 221 years, meaning the two populations almost never co-emerge. This matters because when cicadas with different cycle lengths mate, their hybrid offspring tend to emerge in off-years, alone and without the protective swarm. Predators pick them off easily. Simulation models show that non-prime cycle lengths are eliminated relatively quickly under these conditions, because hybrids from non-prime cycles emerge in higher frequency and get destroyed.
9PubMed. Selection for prime-number intervals in a numerical model of periodical cicada evolutionThe key mechanism is predator satiation. When billions of cicadas appear simultaneously, predators cannot possibly eat them all, so most survive long enough to mate. But a hybrid that emerges on a non-standard year has no swarm to hide in. Modeling work confirms that if hybridization produces offspring with intermediate life-cycle lengths, predation removes those hybrids disproportionately, reinforcing the prime-numbered cycles over evolutionary time.
10PubMed Central. Hybridization selects for prime-numbered life cycles in Magicicada: An individual-based simulation model of a structured periodical cicada populationThe Evolutionary Payoff of Slow Growth
Beyond the prime-number question, there is a broader puzzle: why develop so slowly at all? Plenty of insects manage to grow large in a year or two. The answer ties back to the xylem diet and the demographic math of cicada life. Spending extra years underground is risky because every additional year gives predators, fungi, and soil parasites more time to find and kill you. But extra time feeding also means a larger adult body, which translates directly into higher egg production for females. Life-table analyses of periodical cicadas suggest that for at least some species, the extra fecundity associated with a 17-year development period outweighs the advantages of more frequent reproduction that a shorter cycle would allow.
11PubMed. Evolution of prolonged development: a life table analysis for periodical cicadasIn other words, the tradeoff tips in favor of staying underground longer. A female that takes 17 years to develop can produce and provision more eggs than one that emerges at 13 years. As long as enough nymphs survive the extra four years underground, the population does better in the long run.
12Biological Journal of the Linnean Society. Why cicadas (Hemiptera: Cicadidae) develop so slowlyWhen Things Go Wrong Underground
Cicada nymphs may be well adapted to a slow, quiet life in the soil, but they are far from invulnerable. Their success depends on stable forest habitat with healthy tree roots and undisturbed soil, conditions that are increasingly hard to find in urban and suburban landscapes.
Soil compaction is one of the biggest threats. Compacted soil, common in parks, road medians, and developed areas, is harder for newly hatched nymphs to burrow into and makes it more difficult for mature nymphs to dig their way out when emergence time comes. Research comparing cicada diversity across different urban land uses found that soil compaction from urbanization reduces cicada diversity, apparently by physically preventing nymphs from reaching underground nesting sites.
13PubMed Central. Urban soil compaction reduces cicada diversitySoil contamination is another problem. In areas where construction and demolition waste had been dumped in forested land, researchers tracked cicada nymph populations over several years and found significant year-over-year declines in two species. The contaminated sites also had higher rates of physical malformations in nymphs compared to uncontaminated areas.
14PLoS ONE. Influence of construction and demolition waste on fitness and community structure of cicada nymphs: New bioindicators of soil pollutionLand development poses a more absolute threat. If the trees above a brood’s underground territory are cut down, the nymphs lose their food supply. A parking lot paved over a forest does not just displace cicadas; it eliminates the entire generation developing below. Because periodical cicadas take over a decade to complete a single generation, the loss of a brood in one area can be permanent on any timescale that matters to a human observer. There is no quick rebound when the reproductive cycle is 17 years long.
What Happens Above Ground After They Emerge
After all those years underground, cicadas get only a few weeks as adults. They climb out of the soil, shed their nymphal skin one final time, inflate their wings, and spend roughly four to six weeks mating and, if female, laying eggs. Then they die. The entire adult phase is a sprint: males sing to attract mates, females choose partners and use a saw-like appendage to cut slits in tree branches where they deposit eggs. The eggs hatch a few weeks later, and the tiny first-stage nymphs drop to the ground to begin the cycle again.
This brief aboveground window has ecological consequences that ripple through the forest. When periodical cicadas emerge in massive numbers, their decaying bodies deliver a pulse of nitrogen to the soil. Studies comparing tree growth in emergence years and non-emergence years found that some tree species showed reduced growth during or immediately after emergence, likely because of the physical damage females cause when laying eggs in branches.
15The American Midland Naturalist. The Effect of Periodical Cicadas on Growth of Five Tree Species in Midwestern Deciduous ForestsBut the decomposing bodies of billions of cicadas also act as fertilizer, and longer-term research suggests this nutrient pulse may boost tree growth in the years following emergence. One study detected measurable growth increases in trees that received cicada-derived nutrients, while the damage from egg-laying did not produce a detectable growth reduction at the same sites, raising the possibility that the fertilization effect outweighs the damage in some forest types.
16PubMed. The effects of pulsed fertilization and chronic herbivory by periodical cicadas on tree growthAnnual Cicadas and the Confusion Around Timing
Periodical cicadas get most of the attention, but the majority of the world’s roughly 3,000 cicada species are not periodical. These “annual” cicadas appear every summer in most temperate and tropical regions, and their name is misleading. They are not completing their life cycle in a single year. Most annual cicada species spend two to five years underground as nymphs, feeding on tree roots in exactly the same way periodical cicadas do. They are called annual only because their generations overlap: adults from different cohorts emerge every summer, so you see and hear them each year even though any individual has been underground for several years.
Some non-periodical species take even longer. Certain large cicadas in Australia and South America are thought to spend up to a decade underground, though exact figures are hard to pin down because tracking individual nymphs in soil for years is extraordinarily difficult. The five-nymphal-stage pattern holds for many of these species as well, as confirmed in studies that developed methods to reliably distinguish nymphal stages based on body measurements.
17Journal of Asia-Pacific Entomology. An effective method for accurate nymphal-stage delimitation of the cicada Hyalessa fuscataClimate Change and the Timing of Emergence
Because cicadas depend on seasonal cues from their host trees, and because the final trigger for emergence involves soil temperature, warming climates have the potential to disrupt timing. In spring, periodical cicada nymphs begin moving toward the surface when soil temperatures at their depth reach a threshold, usually in the neighborhood of 18°C (about 64°F). If soils warm earlier in the year than usual, nymphs may be physiologically ready to emerge before the calendar date that their food web expects them.
Modeling work on a non-periodical species, the Lyric Cicada, explored what happens when soil temperatures reach emergence thresholds earlier than the photoperiod cue that normally co-triggers emergence. The simulations found that when warming pushes soil temperatures past the thermal threshold before the day-length trigger kicks in, the photoperiod becomes the controlling factor and essentially overrides the temperature signal.
18Princeton Journal of Pre-Collegiate Research. Climate Driven Disruption of Thermal and Photoperiodic Controls of Cicada EmergenceThat sounds like a safety valve, but it is not clear how far it stretches. Photoperiod is fixed by astronomy and cannot shift with climate, while soil temperatures can keep rising. If the gap between the thermal and photoperiod cues widens enough, the mismatch could eventually push emergence timing into periods when the plants, predators, and other organisms the cicada depends on are out of sync. For periodical cicadas, which already have the longest documented juvenile period of any insect, even small disruptions to the timing of their emergence could have outsized consequences, because the entire survival strategy hinges on precise synchronization across enormous populations.