Are 17-Year Periodical Cicadas Dangerous to Plants?

Periodical cicadas are among the most fascinating insects in North America, known for their extraordinary 17-year life cycle and synchronized mass emergences. These creatures capture the attention of gardeners, farmers, and nature enthusiasts alike every time they appear. However, one frequent concern is whether these cicadas pose a danger to plants. In this article, we’ll explore what 17-year periodical cicadas are, their impact on plants, and how to manage any potential damage.

What Are 17-Year Periodical Cicadas?

Periodical cicadas belong to the genus Magicicada and are unique for their long and highly synchronized life cycles of either 13 or 17 years. The 17-year cicadas emerge en masse from underground where they have spent nearly two decades as nymphs feeding on root fluids. This emergence typically occurs in late spring to early summer when soil temperatures reach around 64°F (18°C).

During their brief adult phase—usually lasting four to six weeks—male cicadas sing loudly to attract females, mate, lay eggs, and then die shortly afterward. The eggs hatch, and the young cicadas drop to the ground where they burrow underground to begin the cycle anew.

The periodicity and sheer numbers of these cicadas make them an evolutionary marvel and a seasonal spectacle. However, their interaction with plants during this cycle raises questions about safety and damage.

How Do Periodical Cicadas Interact with Plants?

Cicadas interact with plants primarily in two ways:

As Nymphs Underground: For most of their lives (13 or 17 years), cicada nymphs feed on xylem fluids from tree roots.
As Adults Above Ground: Adult females cut slits into small branches of trees to lay their eggs.

Feeding as Nymphs

While underground, nymphs attach themselves to the roots of various trees and shrubs, sucking sap for nourishment. Despite living underground for many years, the feeding is generally not harmful to mature trees because the nymphs draw only small amounts of fluid from the roots over long periods.

Research has shown that healthy mature trees tolerate this feeding without significant stress or damage. The root systems are extensive enough to support both the tree’s needs and those of the feeding nymphs.

Egg Laying by Adult Females

The potential for plant damage mainly arises during egg-laying by adult female cicadas. Females use a saw-like ovipositor to create slits or “grooves” in small twigs or branches—usually those less than half an inch thick—to deposit eggs.

This process can cause:

Flagging: Twigs or small branches with eggs may die and fall off as a result of damage.
Twig Mortality: The slitting damages vascular tissues in the twig, leading to its death.
Reduced Plant Vigor: Extensive egg-laying can weaken young or small trees by reducing photosynthetic capacity.

Are Cicadas Dangerous to Plants?

The short answer: Generally no, but there are exceptions depending on plant species, age, size, and cicada population density.

Impact on Mature Trees

Mature trees usually withstand periodical cicada attacks well. The damage caused by egg-laying tends to be limited to small twigs that the tree can easily replace during normal growth cycles.

Examples:

Oak
Maple
Beech
Hickory

These major canopy trees often survive without any long-term harm from cicada emergences.

Impact on Young and Small Trees

Young saplings and small ornamental trees are more vulnerable because:

They have fewer branches so egg-laying damage is relatively more significant.
Loss of multiple twigs may stunt growth.
Stress from repeated flagging may make them susceptible to disease or other pests.

In some cases, heavy cicada egg-laying can kill young trees outright if they cannot compensate for twig loss.

Impact on Agricultural Crops

Most agricultural crops such as corn, wheat, or vegetables do not suffer direct damage from periodical cicadas because they lack woody branches suitable for egg laying.

However, fruit trees like peaches or cherries can experience moderate injury during high population emergences.

How Severe Is Cicada Damage Typically?

Although brood sizes vary widely across geographical regions and years, even massive emergences usually do not cause severe lasting damage to established trees.

Studies show:

Twig flagging rarely exceeds 30% of total branch mass.
Trees recover fully within a growing season.
No significant mortality observed in mature forests after multiple emergences.

Therefore, while visual damage may be striking during peak emergence years due to fallen twigs and loud noise pollution from males calling, ecological impact on plant health is minimal overall.

How Can Gardeners Protect Vulnerable Plants?

For nursery owners, landscapers, or gardeners concerned about young trees or shrubs during periodical cicada years, several practical measures can help minimize damage:

Physical Barriers

Netting: Use fine mesh netting (with holes smaller than ~1/2 inch) over small trees during peak emergence periods (late May through July).
Covers: Temporary plastic covers can protect vulnerable twigs from oviposition but should allow air circulation to avoid heat stress.

Timing Planting

Avoid planting new saplings immediately before anticipated emergence years.
Delay planting until after cicada activity subsides in mid-summer.

Pruning Damaged Branches

After emergence ends, prune out flagging twigs promptly.
This helps prevent secondary infections from fungi or insects invading damaged tissues.

Maintain Tree Health

Healthy trees recover faster; keep plants well-watered and fertilized.
Mulching reduces drought stress which compounds vulnerability.

Should You Worry About Cicadas in Your Garden?

For most home gardeners whose landscape includes mature shade trees and established shrubs, periodical cicadas pose little threat beyond a few unsightly fallen twigs each emergence year. The spectacular event is more a curiosity than a crisis.

If you have young fruit trees or ornamental saplings that you value highly or recently planted just before a predicted emergence, consider protective measures outlined above.

Ecological Benefits of Periodical Cicadas

It’s also worth noting that periodical cicadas provide important ecological services:

Their mass emergences supply abundant food for birds, mammals, reptiles, amphibians, and other insects.
Upon death, decomposing bodies enrich soil nutrients supporting plant growth.

Their root feeding promotes nutrient cycling underground.

These positive effects underscore that periodical cicadas are integral parts of healthy ecosystems rather than pests requiring eradication efforts that could disrupt natural balances.

Conclusion

Seventeen-year periodical cicadas are mostly harmless to plants. While adult females’ egg-laying behavior does cause some twig damage—especially on smaller branches—the effect is generally minor on mature trees which quickly recover. Young saplings may experience more noticeable injury but can often be protected through physical barriers and proper care.

Understanding their biology helps gardeners appreciate this natural phenomenon as part of the environment’s rhythm rather than fear it as a destructive force. With simple precautions when necessary, plants will thrive alongside one of nature’s most remarkable insect spectacles for many generations to come.