Cicadas are best known for their dramatic, noisy emergence. While the sudden appearance of these insects can be overwhelming, their presence is a powerful and necessary force in the landscape. Rather than being a nuisance, the millions of cicadas that emerge perform several ecological functions that structure the health of forests and the wildlife within them.
Essential Protein Pulse for Wildlife
The mass, synchronized emergence of periodical cicadas acts as a sudden, temporary flood of nutrients, often called a “protein pulse,” which benefits nearly all local wildlife. This unique event provides a highly concentrated and easily accessible food source for countless predators, from reptiles and fish to mammals and birds. The sheer volume of this protein allows many animal populations to thrive, with some studies documenting a fourfold increase in short-tailed shrew populations during an emergence year.
Many animals, including raccoons, coyotes, and over 80 species of birds, temporarily switch their primary diet to cicadas. This high-calorie, easily obtainable food source boosts the survival rate of young animals and allows adult predators to dedicate less energy to foraging. The sudden abundance also creates a phenomenon known as “predator satiation,” where the number of cicadas is so massive that predators simply cannot eat them all, ensuring that enough individuals survive to reproduce and perpetuate the cycle.
A secondary benefit is a temporary reprieve for other prey species, such as caterpillars and other insects, that would normally be eaten by birds and small mammals. Because the predators are preoccupied with the easily available cicadas, their usual food sources are left to flourish, which has a positive ripple effect on the ecosystem. This ephemeral pulse of food can lead to a measurable increase in predator populations for one to three years following the emergence.
Natural Soil Aerators and Fertilizers
Cicadas contribute to the health of the soil in two distinct ways: through their emergence and their decomposition. As the nymphs prepare to transform into adults, they tunnel up through the soil from depths of up to two feet, creating pathways for air and water. These dime-sized exit holes, which can number in the hundreds per square meter, effectively aerate compacted soil and significantly improve water infiltration rates, sometimes by as much as 80% in forested areas.
Once the adult cicadas die, their bodies and shed exoskeletons decompose, returning a wealth of concentrated nutrients to the forest floor. The cicada biomass is particularly rich in nitrogen, with bodies containing around 6% nitrogen by dry weight. This decomposition acts as a natural, nitrogen-rich fertilizer, which is released rapidly into the soil and can be quickly taken up by plants. This nutrient return supports the growth of trees and other vegetation, essentially recycling the resources the insects spent years accumulating underground.
Pruning Trees and Shaping Forests
The most visible impact of cicadas is actually a form of natural tree maintenance that helps shape the forest ecosystem. Female cicadas use a specialized structure called an ovipositor to cut small slits into the bark of slender, pencil-width branches where they deposit their eggs. This egg-laying activity weakens the branch tips, causing the leaves to turn brown and die, a condition often referred to as “flagging.”
While this activity can severely damage or even kill young, newly planted trees, it functions differently in a mature forest setting. For large, established trees, the egg-laying is a form of “tip pruning” that removes weak, diseased, or excess growth at the canopy’s edges. By encouraging the tree to shed these outer twigs, the cicadas stimulate the production of new, stronger growth, thereby contributing to the long-term health and structure of the forest.
Cicadas as Scientific Subjects
Beyond their ecological roles, cicadas provide a unique opportunity for scientific study. The emergence of periodical cicadas is tightly linked to soil temperature, typically beginning when the soil at an eight-inch depth reaches 64 degrees Fahrenheit. This temperature dependency makes them excellent bioindicators, allowing scientists to monitor how rising global temperatures and earlier “false springs” associated with climate change are altering their internal biological clocks and emergence timing.
The 13- and 17-year life cycles of periodical cicadas are subjects of evolutionary research, as both are prime numbers. By emerging on prime-numbered cycles, the cicadas minimize the chances of their emergence synchronizing with any short-cycled predator, like a wasp or bird, whose population might otherwise adapt to their presence. Additionally, the sheer volume of their emergence allows researchers to study population dynamics and predator-prey relationships on a massive, yet predictable, scale.