Do 13-Year Periodical Cicadas Affect Tree Health?

Every thirteen years, a remarkable natural phenomenon occurs across large regions of the eastern United States: the emergence of 13-year periodical cicadas. These insects emerge en masse from underground, creating a buzzing symphony that signals their brief above-ground life phase. While their appearances are fascinating and generate significant public interest, many people wonder whether these cicadas pose a threat to the health of trees. In this article, we will explore the biology and life cycle of 13-year periodical cicadas, the nature of their interactions with trees, and whether their emergence has any lasting negative impacts on tree health.

Understanding 13-Year Periodical Cicadas

Periodical cicadas belong to the genus Magicicada. They are unique among insects for their synchronized emergences after spending either 13 or 17 years as nymphs underground. This long developmental period allows them to avoid many predators and produce overwhelming numbers during emergence, a survival strategy known as “predator satiation.”

The 13-year periodical cicadas appear in discrete broods across different geographic areas. The most well-known broods can range from a few million to several billion cicadas per emergence event. After emerging from the soil, adult cicadas live only about four to six weeks. During this time, they mate and lay eggs before dying.

Cicada Life Cycle and Tree Interaction

Underground Phase

For most of their lives, periodical cicada nymphs live beneath the soil surface at depths of about 6 to 24 inches (15–60 cm). They feed on xylem fluid extracted from tree roots. This subterranean feeding is generally not harmful because the volume of fluid extracted is minimal and spread over many roots.

Emergence and Mating Phase

As nymphs mature, they tunnel upward to emerge en masse. Once above ground, adult males sing loudly to attract females. After mating, females use their sharp ovipositors to make slits in small branches and twigs where they deposit eggs.

Egg Laying Damage

The primary way cicadas interact physically with trees occurs during the egg-laying process. Female cicadas cut into young branches—typically one- or two-year-old growth—to create chambers for their eggs. This cutting is called “flagging” because it causes the affected branch tips to wilt and die.

Impact on Tree Health

Immediate Physical Effects: Branch Flagging

The most visible damage caused by 13-year periodical cicadas is flagging of small branches where eggs are laid. These branches often turn brown, wilt, and eventually break off within a few weeks after egg deposition. For healthy mature trees, this damage generally represents only a small percentage of total foliage and branch mass.

Although flagging looks dramatic up close, it rarely affects overall canopy density or photosynthesis enough to stress mature trees seriously. Trees typically respond by producing new growth in subsequent seasons.

Damage to Young Trees and Orchards

While mature trees usually tolerate cicada damage well, young or newly planted trees can be more vulnerable. The loss of numerous young shoots can stunt growth or reduce vigor if an entire small tree’s branches are heavily flagged.

This sensitivity is particularly important in orchards or nurseries where newly planted fruit or ornamental trees are present during periodical cicada emergences. Repeated damage over consecutive years may weaken young trees or reduce fruit yields temporarily.

Long-Term Effects on Tree Health

Research has shown that periodical cicada emergences do not cause long-term harm to forested areas or urban trees. Trees generally recover fully within one growing season as new growth replaces flagged branches.

There is no evidence that cicada feeding or egg-laying introduces disease pathogens into trees or causes permanent structural damage below ground. Periodical cicadas have coexisted with forests for thousands of years without causing lasting declines in tree populations.

Why Do Trees Survive Cicada Emergences?

Several factors explain why trees survive these periodic onslaughts relatively unscathed:

• Localized Damage: Egg laying is limited primarily to small diameter branches rather than trunk or large limbs.
• Short Duration: Adult cicadas are present above ground for only a few weeks.
• Tree Resilience: Trees naturally shed some twigs yearly and can compartmentalize wounds effectively.
• Evolutionary Balance: Periodical cicadas and their host trees have evolved together, leading to a balance where massive cicada emergences do not decimate host populations.

Management Recommendations for Tree Owners

While 13-year periodical cicadas do not threaten mature tree health broadly, homeowners and orchard managers may want to protect vulnerable young trees during emergence years:

• Physical Barriers: Covering young trees with fine mesh netting (less than 1/4 inch) during peak egg-laying periods can prevent females from accessing branches.
• Timing Plantings: Avoid planting young fruit or ornamental trees immediately before anticipated emergences.
• Pruning Flagged Branches: Removing wilted egg-laden branches shortly after emergence can help reduce stress on young trees.
• Maintaining Tree Vigor: Well-watered and fertilized trees recover faster from cicada damage.

Ecological Benefits of Periodical Cicadas

It is worth noting that despite concerns about damage, periodical cicadas provide important ecological benefits that outweigh their temporary nuisance:

• Nutrient Cycling: The mass death of adults provides a significant pulse of nutrients back into forest soils.
• Food Source: Many predators including birds, mammals, reptiles, and other insects rely heavily on cicadas as food during emergence years.
• Soil Aeration: Nymph tunneling helps aerate soils around tree roots.
• Pollination Facilitation: Although they do not pollinate themselves, their activity sometimes flushes out other pollinators in forests.

Conclusion

The arrival of the 13-year periodical cicadas is an awe-inspiring natural event that captures public imagination like few other insect phenomena. While their egg-laying behavior causes some visible branch damage known as flagging—especially on young growth—this does not translate into serious injury for healthy mature trees. Young or recently planted trees may suffer more noticeable impacts but can often be protected with simple management measures.

Overall, research supports that these incredible insects coexist sustainably with their tree hosts over evolutionary time scales. Their periodic emergences represent a fascinating example of nature’s balance rather than a threat to forest or urban tree health. By understanding the biology and effects of periodical cicadas, tree owners can better appreciate these events while taking reasonable steps to safeguard vulnerable plantings during peak emergence years.