Natural Predators That Control 17-Year Periodical Cicada Populations

The 17-year periodical cicada is one of nature’s most fascinating phenomena. Known for emerging en masse every 17 years, these insects can create a spectacular and sometimes overwhelming spectacle in forests and suburban areas alike. Despite their sheer numbers during these emergences, periodical cicadas are subject to various natural predators that play a crucial role in keeping their populations in check. This article delves into the natural enemies of the 17-year periodical cicada, exploring how these predators interact with cicadas and contribute to the balance of ecosystems.

Understanding the 17-Year Periodical Cicada

Before discussing the predators, it’s essential to understand the life cycle and behavior of the 17-year periodical cicada (genus Magicicada). These cicadas spend most of their lives underground as nymphs, feeding on root sap for 13 or 17 years depending on the brood. When the time comes, they emerge synchronously in vast numbers to molt into adults, mate, lay eggs, and die within a few weeks.

This synchronized mass emergence is thought to be an evolutionary strategy known as “predator satiation.” By appearing in overwhelming numbers, cicadas reduce the odds that any individual will be eaten. However, even with this strategy, their populations are still controlled by a variety of natural predators.

The Role of Natural Predators

Natural predators serve an important ecological function by preventing cicada populations from becoming so large that they damage trees or disrupt local ecosystems. Let’s explore some of the most significant natural enemies of 17-year periodical cicadas.

Birds – The Most Visible Predators

Birds are among the primary consumers of adult cicadas during emergence periods. Many bird species take advantage of the sudden availability of easy prey.

Crows and ravens are especially adept at plucking cicadas from branches.

Blue jays, starlings, grackles, and various sparrows are also known to feed heavily on cicadas.
Even larger birds such as hawks may opportunistically consume them.

Birds often exploit cicadas’ noisy mating calls and slow flight to locate and capture them easily. Despite high predation rates by birds during emergence peaks, this only removes a small portion of the millions of cicadas that surface.

Mammals – Opportunistic Feeders

Some mammals take advantage of emergences for a protein-rich meal:

Squirrels frequently climb trees to catch adult cicadas.
Raccoons and opossums may catch them or snatch fallen individuals.

Small rodents also consume nymphs that accidentally surface before emergence.

While mammals may not consume as many cicadas as birds do, their nocturnal or ground-level feeding habits help control different life stages of cicadas.

Reptiles and Amphibians – Less Common But Still Important

Certain reptiles and amphibians prey on cicadas:

Lizards, especially skinks and fence lizards, eat adult cicadas.
Frogs and toads opportunistically feed on adults and fallen individuals.

These predators often benefit from the abundance of cicadas during emergence but typically play a smaller overall role compared to birds.

Insects – Predators Among Predators

Several insect species prey on periodical cicadas at various stages:

Spiders commonly trap adult cicadas in webs.
Praying mantises actively hunt them.

Some species of wasps, such as Scolia dubia, parasitize or kill cicadas.
The infamous cicada killer wasp (Sphecius speciosus) specializes in hunting adult cicadas. Female wasps sting and paralyze cicadas before dragging them back to their burrows as food for their larvae.

Among insect predators, the cicada killer wasp is especially notable because it has evolved specifically to prey upon large cicadas. It helps control adult populations locally around nesting sites.

Fungal Pathogens – Invisible Controls

While not a predator in the traditional sense, fungal pathogens can significantly impact periodical cicada populations by infecting both nymphs underground and adults above ground.

The entomopathogenic fungus Massospora infects adult cicadas, causing debilitating effects that reduce reproductive success before killing them. This fungus spreads rapidly during broods’ emergences and helps regulate population density indirectly by lowering survival and reproduction rates.

Nematodes and Other Parasites

Various nematodes (microscopic roundworms) infect periodical cicada nymphs when they are underground feeding on roots. These parasites weaken nymphs over time and can cause early mortality before emergence.

Other parasite groups such as mites may also infest adult cicadas, further diminishing their fitness during the brief adult stage.

Predator Satiation: A Double-Edged Sword

The mass emergence strategy is designed primarily to overwhelm predators so that enough individuals survive to reproduce. In many ways, it works spectacularly well , billions of adults emerge simultaneously, ensuring successful mating despite intense predation pressure.

However, this abundance also attracts an influx of predators from nearby areas who take advantage of this temporary feast. Predator populations can increase locally during emergence years due to easy access to food but decline again once the brood disappears underground for another 17 years.

This boom-and-bust cycle between prey and predator illustrates a classic ecological dynamic driven by long-term evolutionary adaptations.

Ecological Importance of Cicada Predators

The relationship between periodical cicadas and their natural predators has several ecological implications:

Food web support: Cicada emergences provide a major food resource that boosts predator populations such as birds, mammals, reptiles, insects, and fungi.

Nutrient cycling: Predation results in carcasses that decompose quickly, recycling nutrients back into forest soils.
Population control: Natural enemies prevent excessive defoliation or damage caused by huge numbers of egg-laying females cutting slits in tree branches.
Biodiversity maintenance: Diverse predator species help maintain balance within forest ecosystems where periodical cicadas emerge regularly.

Conclusion

Though 17-year periodical cicadas appear invincible due to their staggering numbers and synchronized emergence cycle, they face considerable pressures from an array of natural predators including birds, mammals, reptiles, insects like the specialized cicada killer wasp, fungi, nematodes, and other parasites. These biological controls contribute significantly to regulating population sizes over time and maintaining ecological equilibrium within forest habitats.

Understanding these predator-prey interactions enhances our appreciation for nature’s complexity and highlights how even seemingly unstoppable phenomena like mass-cicada emergences are subject to intricate checks from other living organisms. As science continues to explore these relationships further, we gain valuable insights into ecosystem dynamics shaped across millennia by evolution’s hand.

References available upon request.