The emergence of cicadas, especially the massive synchronized arrival of periodical broods like Magicicada, often sparks public concern over the safety of local trees. These insects spend most of their lives underground, surfacing in huge numbers for a short period of mating and egg-laying, creating a dramatic natural event. While annual cicadas appear every summer in smaller groups, the dense, noisy emergence of their 13- or 17-year counterparts raises a high-stakes question for homeowners: Do these insects pose a fatal threat to the surrounding landscape? This question focuses on the physical damage cicadas inflict on woody plants during their brief adult phase.
The Immediate Answer: Assessing Fatal Risk
Generally, healthy, mature trees are not killed by cicada activity. Adult trees possess enough foliage and branch mass to easily withstand the loss of numerous small branch tips. The damage seen on large trees is essentially a form of natural pruning that does not affect the tree’s overall long-term health or survival rate.
However, the risk shifts dramatically for smaller, younger, or stressed trees, which can suffer severe or even fatal damage during a heavy emergence. These vulnerable trees have a high proportion of branches with the exact diameter preferred by egg-laying females. The resulting widespread damage can overwhelm a small tree’s limited resources, leading to canopy loss and the introduction of pathogens. The most visible sign of cicada damage is “flagging,” where the tips of branches turn brown and die.
The Mechanism of Damage: Oviposition
The mechanism that causes tree damage is the female cicada’s egg-laying process, known as oviposition, not feeding. Female cicadas do not eat tree leaves or branches; they use a sharp, specialized organ called an ovipositor to slice into the wood. They cut narrow slits, parallel to the branch’s long axis, to create an “egg nest” where they deposit dozens of eggs.
A single female can repeat this process multiple times, laying up to 600 eggs during her short lifespan. This repeated slitting severs or disrupts the vascular tissue in the branch. The damage interrupts the flow of nutrients and water to the tip of the branch, causing the portion beyond the slit to wither, die, and turn brown, resulting in the characteristic flagging.
Identifying Vulnerable Trees and Species
The primary factor determining a tree’s vulnerability is its size, age, and branch diameter, regardless of the species. Trees planted within the last few years or newly planted saplings are at the highest risk of irreparable harm. Female cicadas seek out branches that are roughly the diameter of a pencil, generally between 1/8 inch and 1/2 inch, for egg deposition.
Cicadas will use many kinds of woody plants, but certain deciduous species are favored targets due to their branch structure. Highly susceptible trees include fruit trees, such as cherry and pear, as well as landscape favorites like maples, oaks, willows, and dogwoods. Conifers are typically avoided because their sap or needles interfere with the egg-laying process.
Protecting Trees During Emergence
The most effective method for protecting high-risk trees is the use of physical barriers, as chemical insecticides are often ineffective against the waves of emerging adults. Homeowners should cover young or vulnerable trees completely with fine mesh netting before the cicadas begin to lay eggs, typically in May. The netting must have a mesh size of 1/4 inch or smaller to physically block the insects from accessing the branches.
The netting should be draped over the entire canopy and securely fastened at the base of the trunk to prevent cicadas from crawling up from the ground. Additionally, postpone any major pruning until after the emergence has ended, usually after six weeks, to reduce the number of fresh, susceptible branch tips. Maintaining overall tree health through adequate watering and mulching also helps the tree better tolerate and recover from any stress or damage.