In the eastern United States, a remarkable biological phenomenon unfolds with clockwork precision. Every 17 years, the forest floor trembles as billions of periodical cicadas emerge simultaneously from their underground sanctuary. These insects have spent nearly two decades in darkness, feeding on tree root sap and biding their time. When soil temperatures reach approximately 64 degrees Fahrenheit, typically in late April or May, they tunnel upward toward sunlight. What follows is one of nature’s most spectacular mass emergences – a biological event that transforms landscapes, overwhelms predators, and captures human imagination. The deafening chorus of male cicadas, the trees draped with their shed exoskeletons, and the sheer abundance of these red-eyed insects create an experience that is both awe-inspiring and unmistakable.
The Extraordinary Life Cycle of Periodical Cicadas
Periodical cicadas (Magicicada spp.) have perhaps the most unusual life cycle of any insect in North America, with the longest juvenile development period. After hatching from eggs laid in tree branches, the tiny nymphs drop to the ground and immediately burrow into the soil. There, they will spend the next 17 years (or 13 years for southern broods) living underground, passing through five developmental stages while feeding on xylem fluids from tree roots. When their lengthy underground development concludes, the final-stage nymphs construct exit tunnels to the surface, emerging in synchrony with millions of their brethren. Above ground, their adult lifespan lasts just 4-6 weeks – a brief, frenzied period of mating and reproduction before the cycle begins anew.
The Science of Synchronicity: Why 17 Years?
The 17-year emergence cycle of periodical cicadas has fascinated scientists for generations, prompting research into why such an unusual prime-numbered life cycle evolved. Most experts believe that the prime-numbered cycles (either 13 or 17 years) represent an evolutionary strategy to avoid synchronizing with predator population cycles. Because prime numbers have few divisors, cicadas emerging every 17 years are less likely to coincide with predator population booms that might occur in cycles of 2, 3, or 4 years. This mathematical protection provides a survival advantage, as predators cannot easily anticipate and adapt to these infrequent emergences. Additionally, the synchronized emergence creates a “predator satiation” effect – producing so many cicadas simultaneously that predators cannot possibly consume them all, ensuring enough survivors to reproduce.
Broods: Nature’s Calendar-Keepers
The periodical cicadas of eastern North America are organized into distinct groups called “broods,” each with its own geographic range and emergence schedule. Scientists have identified 12 different 17-year broods (numbered using Roman numerals I through XVII, with some numbers missing) and 3 different 13-year broods. Each brood emerges in its specific year and generally maintains its geographic boundaries, though some overlap can occur. The largest and most widely distributed is Brood X (the “Great Eastern Brood”), which emerges across 15 states from Georgia to New York and west to Illinois. When not experiencing a major emergence, a given location typically sees these cicadas only once every 13 or 17 years, making each event a generational milestone for human observers.
The Visual Spectacle: Identifying Periodical Cicadas
Periodical cicadas are immediately recognizable and distinct from their annual cicada cousins that appear every summer. Measuring between 1 and 1.5 inches in length, these insects possess a black body, striking red-orange eyes, and transparent wings with prominent orange veins. Their emergence begins with the appearance of distinctive exit holes in the soil, approximately 1/2 inch in diameter, which can number up to 1.5 million per acre in densely populated areas. As night falls, nymphs climb vertical surfaces – tree trunks, fence posts, walls, even curious observers – where they undergo their final molt. By morning, forests are decorated with countless empty exoskeletons, clinging to surfaces as the newly emerged adults move to the tree canopy. This transformation from soil-dwelling nymph to winged adult happens en masse, creating surreal landscapes where every surface may be covered with cicadas.
The Deafening Chorus: Acoustics and Communication
Perhaps the most memorable aspect of a periodical cicada emergence is the overwhelming sound produced by millions of males singing simultaneously to attract females. Using specialized structures called tymbals – ribbed membranes on their abdomens that they flex and relax rapidly – male cicadas create their distinctive calls. Each of the seven species of periodical cicadas has its own unique acoustic signature, allowing females to identify appropriate mates amid the cacophony. In areas of high cicada density, the combined chorus can reach an astonishing 100 decibels – comparable to a chainsaw or motorcycle – making normal conversation difficult and creating a persistent soundtrack that defines the emergence season. This acoustic phenomenon typically peaks during mid-morning and late afternoon when temperatures are optimal for cicada activity.
The Seven Species: A Synchronized Community
What appears to casual observers as a single cicada emergence actually involves up to seven distinct species emerging simultaneously. The 17-year cicadas comprise four species – Magicicada septendecim, M. cassini, M. septendecula, and the recently recognized M. neotredecim – while three species follow a 13-year cycle. These species have evolved to emerge together, creating an extraordinary example of convergent timing despite their genetic differences. Each species occupies slightly different ecological niches within the forest habitat, with variations in their preferred egg-laying sites, song patterns, and even body size. This cooperative emergence represents a remarkable example of how multiple species can evolve to take advantage of the same predator-avoidance strategy, maximizing survival through synchronized life cycles despite being separate species.
Ecological Impact: How Forests Respond to Cicada Emergences
The mass emergence of periodical cicadas creates significant but generally beneficial ecological impacts on eastern forests. When female cicadas lay eggs, they create small slits in young tree branches, which can cause a phenomenon called “flagging” – the browning and breaking of branch tips. While this natural pruning may temporarily affect a tree’s appearance, it rarely causes long-term damage to mature trees and may actually stimulate future growth. More importantly, the death of billions of cicadas following their brief adult lifespan results in a massive nutrient pulse to the forest ecosystem. Their decomposing bodies provide a substantial nitrogen fertilization effect, benefiting soil microorganisms, fungi, and ultimately the trees themselves. Research has shown measurable increases in forest growth following major cicada emergences, demonstrating how this 17-year cycle has become integrated into the broader ecosystem dynamics.
Cultural Significance: Human Responses Through History
Periodical cicada emergences have fascinated and sometimes alarmed human observers throughout American history, generating a rich cultural legacy. Native American tribes incorporated cicadas into their oral traditions, often viewing the insects as symbols of resurrection and renewal. Early European colonists sometimes misinterpreted the emergences as biblical plagues of locusts, documenting their fear and wonder in journals and correspondence. By the 19th century, scientists had begun systematically studying the cicadas’ unusual life cycle, with naturalist Charles Marlatt establishing the brood numbering system still used today. In contemporary America, cicada emergences have inspired everything from festivals and culinary experiments to art installations and citizen science projects. Communities throughout the eastern United States often mark time by these emergences, with many residents remembering where they were during the last appearance 17 years earlier.
Cicadas as Food: The Predator Buffet
The sudden abundance of periodical cicadas creates a rare feast for wildlife across the eastern United States. Birds such as grackles, robins, and woodpeckers gorge themselves on the protein-rich insects, often becoming visibly selective as they learn to target the nutrient-dense abdomens. Mammals including squirrels, raccoons, opossums, and even domestic dogs and cats take advantage of this easy prey source, sometimes eating so many cicadas that they temporarily alter their normal foraging behaviors. Fish eagerly strike at cicadas that fall into streams and lakes, providing exceptional fishing opportunities during emergence periods. Even predatory insects and spiders benefit from the bounty, though they make a negligible impact on the overwhelming cicada population. This temporary abundance creates what ecologists call a “resource pulse” that ripples through multiple trophic levels of the ecosystem, potentially affecting predator populations for years following an emergence.
Cicadas in the Kitchen: Edible Insects
Periodical cicadas represent one of North America’s most accessible opportunities for entomophagy – the practice of eating insects. Nutritional analyses have shown that cicadas are rich in protein, low in fat, and contain various minerals, making them comparable to other lean meats. The best time to harvest cicadas for culinary purposes is just after they’ve emerged from their nymphal shells but before their exoskeletons have hardened, when they’re known as “tenerals” and have a softer texture. Various recipes have been developed for preparing cicadas, from simple methods like roasting or sautéing to more elaborate preparations including cicada tacos, cicada stir-fries, and even cicada desserts. Those interested in trying cicadas should be aware that the insects may concentrate small amounts of mercury and should be avoided by people with shellfish allergies due to similar proteins found in both organisms.
Climate Change and Cicada Cycles
The clockwork precision of periodical cicada emergences makes them valuable bioindicators for studying climate change impacts. Scientists have documented instances of accelerated development in some cicada populations, with small groups emerging up to four years ahead of their expected schedule – a phenomenon termed “stragglers” when individuals emerge early. Research suggests that warming temperatures may be allowing nymphs to reach maturity faster by extending their annual feeding period. The geographic ranges of some broods also appear to be shifting northward as climate zones migrate. Long-term monitoring of these changes provides researchers with insights into how climate change affects developmental timing in insects with extended life cycles. Given their sensitivity to soil temperature cues for emergence, periodical cicadas may serve as early warning systems for broader ecological disruptions caused by changing climate patterns.
Protecting Your Garden: Managing Cicada Impacts
While periodical cicadas rarely cause significant damage to established landscapes, newly planted trees and shrubs can be vulnerable to egg-laying damage. Horticulturists recommend delaying new plantings of susceptible woody plants until after an expected emergence in your area. For existing young trees (typically those with stems less than 1/2 inch in diameter), protective measures may include covering plants with fine netting (1/4-inch or smaller mesh) during the 4-6 week adult cicada season. Chemical insecticides are generally discouraged for cicada management, as they have limited effectiveness against such massive populations and can harm beneficial pollinators and other wildlife. Professional arborists sometimes recommend a technique called “flagging prune,” where damaged branch tips are removed after egg-laying is complete, though this is usually unnecessary for established trees. The most sustainable approach recognizes that cicadas have co-evolved with eastern forests for millennia, and temporary aesthetic damage is outweighed by the ecological benefits they provide.
Citizen Science: Tracking the Swarms
The predictable yet geographically expansive nature of periodical cicada emergences makes them ideal subjects for citizen science initiatives. Projects like Cicada Safari, developed by Mount St. Joseph University, enable smartphone users to photograph and report cicada sightings, contributing valuable data about emergence timing and geographic boundaries. The University of Connecticut’s Cicada Watch similarly engages public participants in mapping emergence patterns. These crowdsourced observations help scientists document how brood distributions may be changing over time due to land use changes, climate shifts, or other factors. For many participants, contributing to cicada monitoring becomes a multi-generational family activity, with grandparents sharing memories of previous emergences while helping younger generations document the current event. This blend of scientific contribution and cultural tradition has made cicada tracking one of North America’s most successful and enduring citizen science programs.
Awaiting the Next Emergence: Predicting Future Swarms
The predictable nature of periodical cicada emergences allows scientists and cicada enthusiasts to anticipate future events with remarkable precision. Detailed maps and schedules for all known broods enable residents throughout the eastern United States to know when to expect these insects in their specific location. For those who have experienced a emergence firsthand, the 17-year wait creates a special form of anticipation – parents tell children stories of the strange red-eyed insects that will appear when they’re teenagers, and property owners consider the timing of young tree plantings. Researchers continue refining emergence predictions by incorporating climate data and citizen science observations from previous cycles. As each brood’s expected emergence year approaches, public education campaigns help communities prepare for and appreciate this extraordinary natural spectacle that has played out for millennia across eastern forests.
Conclusion
The 17-year periodical cicadas represent one of North America’s most extraordinary natural phenomena – a living time capsule that connects generations of both insects and human observers. Their prime-numbered life cycle, massive synchronized emergence, and ecological impact make them unique among the world’s insects. As climate change and habitat fragmentation pose new challenges to these ancient species, continued research and public appreciation become increasingly important. Whether experienced as a deafening chorus in suburban backyards, a nutritional windfall for forest ecosystems, or a subject of scientific study, the periodical cicadas remind us of nature’s remarkable adaptations and the enduring cycles that connect past, present and future. When the soil warms and the cicadas rise again, they offer us a rare opportunity to witness biological synchronicity on a continental scale – a 17-year swarm truly like no other.