Homeowners and nature enthusiasts often pause at the sight of a cicada clinging to bark or hear the buzz of their chorus in the summer heat, immediately wondering if these loud insects will kill their trees. The short answer is that healthy trees usually survive a cicada emergence, though the story is more nuanced for younger or stressed plants. Understanding the lifecycle of these insects and the specific ways they interact with bark and roots reveals why panic is often unnecessary and targeted care is the better response.
The Lifecycle and Feeding Habits of Cicadas
Cicadas are divided into two primary categories: annual and periodical, and their behavior dictates the level of threat to trees. Annual cicadas, which appear every year, spend most of their lives underground as nymphs feeding on root sap before emerging to molt and reproduce. Periodical cicadas, however, follow a much longer schedule, with some broods emerging only once every 13 or 17 years. During their brief adult phase, which lasts just four to six weeks, cicadas focus almost entirely on reproduction rather than feeding on tree foliage.
How Nymphs Affect Root Systems
The real interaction with trees happens below ground, where the nymph stage occurs. Cicada nymphs burrow through the soil and latch onto the roots of trees and shrubs to feed on the sap that carries nutrients upward. While this might sound destructive, research indicates that the feeding is generally light and does not remove enough sap to kill a mature, established tree. The root system of a large tree is so vast that the minor damage caused by nymph feeding is often indistinguishable from the natural wear and tear of soil erosion and microbial activity.
The Impact of Egg-Laying on Branches
The primary damage caused by cicadas occurs when females lay their eggs. Using a saw-like ovipositor, a female cuts a small slit in the bark of a twig to deposit her eggs. This process creates a wound that can interrupt the flow of nutrients, effectively cutting off the twig beyond the incision. While this results in the death of numerous small branches—known as "flagging"—it is largely a cosmetic issue for large, established trees. The tree itself usually survives because the energy reserves in the roots and main trunk remain intact.
Young Trees Require Protection
Not all trees are resilient enough to shrug off the cicada’s reproductive strategy. Newly planted trees and saplings lack the mass and energy reserves of mature specimens, making them vulnerable to the stress of heavy egg-laying. If a young tree loses a significant portion of its canopy to flagging, it can struggle to photosynthesize and grow. In these cases, protective measures are essential to ensure the tree establishes a strong foundation before facing the insects again years later.
Protecting Vulnerable Trees
Homeowners who want to safeguard small or valuable trees have a few practical options to prevent cicada damage. The most effective method is to cover the tree with a fine-mesh netting, such as bird netting or row cover, to physically block the insects from reaching the branches. This barrier must be installed before the adults begin to emerge and secured tightly at the base to prevent cicadas from crawling underneath. Removing the netting after the adults have died off and the eggs have hatched allows the tree to benefit from sunlight and rain without trapping moisture.
Timing and Tree Health
Proactive tree care plays a significant role in surviving a cicada emergence. Trees that are already stressed from drought, disease, or poor soil are less capable of recovering from the shock of egg-laying. Ensuring trees receive adequate water during dry periods and are mulched to retain moisture can bolster their resilience. A healthy tree can compartmentalize the wounds caused by cicadas, sealing them off over time and preventing long-term damage to the trunk or major limbs.
