Insects

Why do cicadas emerge from the ground only every 17 years?

Why Do Cicadas Emerge From The Ground Only Every 17 Years

Cicadas are intriguing insects primarily known for their unique life cycle, particularly the periodical cicadas that emerge every 17 years.

Their emergence is a strategic survival tactic, allowing them to outlast predators and maximize their breeding success.

These creatures spend most of their lives underground as nymphs, feeding on plant roots and maturing in the darkness.

A dense forest floor with small holes scattered throughout.

Cicadas emerging from the ground in large numbers, climbing up tree trunks to shed their exoskeletons

Different broods of cicadas emerge at varying intervals, with some emerging every 13 years.

This staggering of emergence times means that regions often experience cicada activity nearly every summer, even if not all cicadas are from the same brood.

The synchronization of their life cycles, dictated by years of evolution, plays a crucial role in ensuring that there are enough cicadas to mate, lay eggs, and return underground before the cycle begins again.

Understanding these fascinating patterns of emergence sheds light on the ecological strategies that cicadas employ.

As cicadas prepare to resurface, their arrival can transform summer landscapes, generating a symphony of sounds that exhilarates nature enthusiasts and scientists alike.

The Mysterious Life Cycle of Periodical Cicadas

A dense forest floor with cicada nymphs emerging from the ground, surrounded by tall trees and the sound of buzzing cicadas in the air

The life cycle of periodical cicadas is marked by significant phases, primarily spent underground as nymphs before they emerge as adults.

This cycle spans either 13 or 17 years, with synchronized emergence leading to dramatic population displays.

Growth and Development Underground

Periodical cicadas begin their journey as eggs laid in tree branches. After about six to ten weeks, these eggs hatch, releasing small nymphs.

The nymphs fall to the ground and burrow down to feed on the sap from plant roots.

This underground stage is crucial, lasting anywhere from four to up to 17 years.

During this time, they molt several times, shedding their exoskeletons as they grow.

Each molt represents a significant growth phase, as the nymphs develop into larger and more mature stages.

The environment, including soil temperature and moisture, influences their growth, marking the passage of time in their hidden lives.

Transformation and Emergence

As the nymphs approach maturity, they begin to prepare for emergence.

This phase is closely tied to environmental conditions, particularly temperature and day length.

When the time is right, nymphs tunnel back to the surface in large numbers, usually synchronized across an entire brood.

Emerging en masse reduces predation, as the sheer volume overwhelms natural predators.

Once above ground, nymphs undergo a final transformation into adults.

Their bodies expand, and wings unfurl, leaving behind a discarded exoskeleton.

This emergence, linked to the 17-year cycle, leads to a remarkable spectacle as millions of cicadas light up their environments.

Reproduction and Egg-Laying

Once transformed into adults, cicadas have a brief window for reproduction.

Their main objective is mating and laying eggs, which will ensure the next generation’s survival.

Males produce distinctive mating calls to attract females, creating a symphony of sound during the summer months.

After mating, females lay their eggs in slits they create in tree branches.

This process takes place several weeks after emergence and involves about 30 to 400 eggs per female.

Once the eggs hatch, the cycle begins anew, with the nymphs dropping to the ground and burrowing to commence their long, subterranean life.

This cyclical process ensures that every few years, specific broods of cicadas emerge, creating a rhythm in nature that captures attention.

Cicada Survival Strategies and Environmental Impact

A dense forest floor with cicada nymphs emerging from the ground, surrounded by leaf litter and tree roots.

Some nymphs are climbing up tree trunks while others are shedding their exoskeletons

Cicadas employ various strategies for survival and significantly influence their ecosystems.

Their unique life cycle and emergence patterns have evolved to enhance their chances of survival, while their brief adult life contributes to the richness of forest ecosystems.

Evading Predators Through Synchronized Emergence

Synchronized emergence is a key survival strategy for cicadas. Billions of cicadas typically emerge at once, overwhelming potential predators.

This phenomenon, called predator satiation, diminishes the chances of individual cicadas being eaten.

During these mass emergence events, predator species such as birds, amphibians, and insects struggle to consume enough cicadas to impact the population.

Furthermore, the sheer number of cicadas can lead to lower predation rates on any single cicada, allowing many to survive long enough to mate and reproduce.

Contribution to the Ecosystem

Cicadas play a crucial role in forest ecosystems.

As they emerge, they feed on the sap from tree roots, causing minimal damage. Their feeding helps facilitate nutrient cycling in the soil.

After mating, the females lay eggs in tree branches, where the nymphs drop to the ground and burrow into the soil.

This process aerates the soil and contributes organic matter, benefiting surrounding plants.

The decaying bodies of cicadas also add nutrients back into the ecosystem, fostering plant growth.

The Phenomenon of Stragglers

While most cicadas follow a strict cycle of 13 or 17 years, some stragglers emerge in years outside of this cycle.

These outliers may emerge due to environmental factors, such as warmer temperatures, which can confuse usual patterns.

Stragglers may not benefit from the advantages of synchronized emergence. Their survival rates can be lower, as they face heightened predation risks.

Still, stragglers add genetic diversity to cicada populations and may serve as a resource for predators during off years.

Distinct Cicada Broods and Their Impact

Different cicada broods, such as Brood X, have distinct life cycles and geographical distributions.

Each brood emerges at specific times, helping to ensure that not all cicadas are at risk from similar environmental threats simultaneously.

The staggered emergence patterns of various broods also help maintain a balanced ecosystem.

By avoiding complete synchrony, these broods reduce competition for resources among themselves and contribute to a structured dynamic in predator-prey relationships.

Each brood’s specific timing further supports diverse biological interactions within their habitats.

Frequently Asked Questions

A group of cicadas emerging from the ground in a forest after 17 years, surrounded by trees and foliage

Cicadas, particularly the 17-year variety, have unique life cycles that prompt many questions.

Understanding their emergence process, environmental influences, and developmental stages provides insight into their fascinating biology.

How do 17-year cicadas calculate their long underground period?

Cicadas spend a significant portion of their lives underground, primarily as nymphs.

They are believed to track their time using a combination of soil temperature and the amount of sap from roots they consume.

This timing mechanism allows them to synchronize their emergence with specific environmental conditions.

What environmental signals prompt cicadas to emerge after 17 years?

As cicadas mature underground, they respond to environmental cues. Changes in temperature and humidity often signal that it is time to emerge.

Typically, they begin to surface when the ground temperature reaches around 64 degrees Fahrenheit, often coinciding with late spring or early summer.

In what ways do cicadas benefit from such an unusual life cycle?

The long life cycle of cicadas serves several purposes.

By emerging in large numbers at once, they overwhelm predators, ensuring that many will survive to reproduce.

This strategy increases their chances of successfully mating and laying eggs, contributing to the population’s longevity.

Can you explain the lifecycle stages of 17-year cicadas?

The life cycle of a 17-year cicada consists of several stages. It begins with eggs laid in tree branches, which hatch into nymphs.

Nymphs drop to the ground and burrow, where they spend years feeding on tree roots.

After 17 years, they emerge, molt, and become adults, ready to find mates and continue the cycle.

What distinguishes the 17-year cicada from its 13-year counterparts?

The main difference between 17-year and 13-year cicadas lies in their life cycle length and instar stages.

17-year cicadas typically take longer to reach maturity compared to their 13-year cousins.

This variation allows for a staggering of emergences, which minimizes competition and enhances survival.

Why might I hear cicadas annually if some only emerge every 17 years?

Some cicada species emerge on different schedules, including annual cycles.

This overlapping emergence allows for the sounds of cicadas to be present almost every year, creating a symphony of sounds during the warmer months.

About the author

Sophia

Meet Sophia, our marvelous mammal expert! Sophia has a deep love for furry friends, from the tiny shrew to the giant elephant. She spends her days studying how these incredible creatures live, play, and interact with their environment. With a heart full of curiosity and compassion, Sophia is dedicated to protecting mammals and their habitats. Join her as she shares fun facts and exciting discoveries about the wonderful world of mammals!