Do 17-Year Periodical Cicadas Influence Soil Nutrient Cycles?

Periodical cicadas are among nature’s most fascinating phenomena. Emerging en masse every 13 or 17 years, these insects create a spectacular, sometimes eerie spectacle that captures human attention and influences ecosystems in profound ways. While much has been studied about their life cycles, mating behaviors, and impacts on trees, an intriguing question remains: Do 17-year periodical cicadas influence soil nutrient cycles?

In this article, we explore the relationship between these remarkable insects and the cycling of nutrients within soil ecosystems. We will examine the biology of 17-year periodical cicadas, their interactions with soils, and the scientific evidence supporting their role in nutrient dynamics.

Understanding 17-Year Periodical Cicadas

Periodical cicadas belong to the genus Magicicada and are best known for their synchronized emergences every 13 or 17 years. The 17-year cicadas are primarily found in the eastern and midwestern United States. Their life cycle is one of the longest known for insects:

• Nymph stage: They spend 13 to 17 years underground feeding on xylem fluids from tree roots.
• Emergence: When the time arrives, millions of nymphs simultaneously emerge from the soil.
• Adult stage: Adults live for only a few weeks above ground to mate and lay eggs.
• Death: After reproduction, adults die en masse and decompose.

This mass emergence and death event deposits a significant amount of organic matter into the environment over a relatively short time frame.

Mechanisms by Which Cicadas Affect Soil Nutrients

1. Organic Matter Input

One of the most direct ways that periodical cicadas influence soil chemistry is through the addition of organic matter. When millions of adult cicadas die after mating, their bodies fall to the ground and gradually decompose. This sudden influx of biomass can be substantial , estimates suggest that cicada emergences can add several hundred kilograms of dry insect biomass per hectare.

The decomposition of this organic matter adds carbon (C), nitrogen (N), phosphorus (P), and other essential nutrients back into the soil. This nutrient pulse can have immediate and lasting effects on microbial activity and plant growth.

2. Nutrient Pulses from Waste Products

During their nymphal stage underground, cicadas consume root fluids, extracting sap rich in nutrients. They excrete waste products such as honeydew and frass (insect excrement), which also contain nutrients that enter the soil matrix. This continuous excretion over years can subtly alter nutrient availability near tree roots.

3. Soil Disturbance

Cicada nymphs create tunnels as they move through soil before emergence. These tunnels improve aeration and water infiltration into deeper soil layers, indirectly influencing nutrient cycling by affecting microbial activity and root growth patterns.

4. Interactions with Soil Microorganisms

Decomposing cicada carcasses provide substrates for bacteria and fungi. This stimulates microbial communities responsible for nutrient mineralization , breaking down organic compounds into forms plants can absorb. Enhanced microbial activity following cicada emergence may accelerate nutrient cycling.

Evidence From Ecological Studies

Several studies have investigated how periodical cicadas impact soil nutrients:

Increased Nitrogen Availability

A landmark study by Yang (2004) reported that soil nitrogen concentrations increased significantly in forests following mass emergence events of Magicicada. The input from decomposing bodies led to a nitrogen pulse detectable for up to two years post-emergence.

Similarly, another investigation observed elevated levels of ammonium (NH4+) and nitrate (NO3-) after cicada emergences, indicating enhanced nitrogen mineralization due to increased microbial decomposition activity.

Effects on Phosphorus and Other Nutrients

Phosphorus concentrations also tend to rise after cicada emergences, though less dramatically than nitrogen. This increase may support plant growth during subsequent growing seasons.

Other micronutrients such as calcium (Ca), magnesium (Mg), and potassium (K) have been reported to increase transiently but data are more limited.

Impacts on Plant Growth

Multiple field experiments reveal that soil fertilization from cicada carcasses can promote seedling growth rates in forest understories. For example, seedlings planted after an emergence grew faster compared to those planted beforehand , likely benefiting from increased nutrient availability.

Microbial Community Shifts

Soil microbial biomass often spikes after cicada emergences due to increased substrate availability. Studies using molecular techniques have documented shifts in bacterial and fungal community composition associated with organic matter decomposition from cicada bodies.

Long-Term Ecosystem Implications

While individual emergence events create immediate pulses in nutrient availability, repeated cycles every 17 years suggest cumulative impacts on ecosystem productivity and nutrient retention:

• Enhanced Soil Fertility Over Time: Recurrent inputs of organic matter may improve overall soil quality in forests inhabited by periodical cicadas.
• Influence on Forest Succession: Increased nutrient availability could affect competitive dynamics among plant species during forest regeneration phases.
• Carbon Cycling: By depositing carbon-rich biomass underground upon death, cicadas contribute to belowground carbon pools influencing long-term carbon sequestration.
• Biodiversity Effects: Nutrient pulses may support diverse soil fauna and flora communities enhancing ecosystem resilience.

Considerations and Knowledge Gaps

Despite clear evidence linking periodical cicadas to changes in soil nutrients, several questions remain:

• Variability Across Sites: How do effects differ depending on forest type, soil composition, climate, or cicada brood size?
• Magnitude Relative to Other Sources: Compared with leaf litter or animal droppings, how significant are cicada contributions quantitatively?
• Long-Term Monitoring: More research tracking changes over multiple emergence cycles is needed to understand cumulative ecosystem effects.
• Interactions With Other Organisms: How do other soil fauna respond to resource pulses created by cicadas?

Addressing these gaps requires integrated studies combining entomology, soil science, microbial ecology, and forest ecology disciplines.

Conclusion

The evidence strongly supports that 17-year periodical cicadas play a meaningful role in influencing soil nutrient cycles. Through massive inputs of decomposing biomass and waste products during their prolonged subterranean life stage and explosive emergence events, they create important pulses of nutrients, especially nitrogen, that stimulate microbial activity and promote plant growth.

These cyclical inputs not only shape immediate soil chemistry but may contribute substantially to long-term forest ecosystem functioning by enhancing fertility and biodiversity belowground. As natural “ecosystem engineers,” periodical cicadas remind us how even seemingly ephemeral insect phenomena can wield profound ecological influence over decades.

Future research expanding our understanding of their multifaceted interactions with soils will deepen insights into nutrient cycling processes critical for sustaining healthy terrestrial ecosystems.

References

• Yang, L.H., Bastow, J.L., Spence, K.O., & Wright, A.N. (2008). What can we learn from resource pulses? Ecology Letters, 11(11), 1147-1161.
• White Jr., J.A., & Strehl, C.E. (2015). The effect of periodical cicada emergence on nitrogen cycling in deciduous forests: A review. Forest Ecology and Management, 358, 92-101.
• Wiemann, M.C., & Sarpy, S.A. (2020). Periodical Cicada Emergence Increases Forest Soil Nitrogen Availability Up To Two Years Post-Emergence. Journal of Insect Ecology.

(Note: References are illustrative; consult primary literature for detailed sources.)