Cicadas are insects well-known for their long, synchronized life cycles and the extremely loud chorusing noises produced by the males during mating season. These insects rely on plants for sustenance throughout their entire lives, consuming fluids rather than chewing on tissue like many other pests. Cicadas do feed on plant sap, but this activity is typically not the primary cause of noticeable damage to healthy, established vegetation. The most significant harm to trees and shrubs comes from a different activity entirely, which affects specific parts of the plant.
How Cicadas Feed
Cicadas possess specialized mouthparts structured for tapping into a plant’s vascular system. This apparatus is a rigid, straw-like structure called a rostrum, which functions like a needle to pierce the outer layers of the plant tissue. They specifically target the xylem, the plant tissue responsible for transporting water and dissolved minerals from the roots throughout the tree.
The insects extract xylem sap, a fluid generally low in nutritional value, meaning they must consume large quantities to meet their dietary needs. Nymphs spend years underground, where they attach to tree roots and feed exclusively on the sap found there.
Once they reach the adult stage and emerge, they continue this sap-feeding behavior, shifting their focus to the stems and young twigs above ground. Because the xylem system is high-volume, a mature, healthy plant can generally tolerate the fluid loss caused by adult cicada feeding without showing signs of stress. This consumption rarely results in substantial, long-term harm to established trees.
Plant Damage Caused by Cicadas
While the feeding process causes little concern for mature trees, the activity of egg-laying creates the most visible and lasting damage to plants. This activity, known as oviposition, is carried out by the adult female cicada after mating. She uses a sharp, saw-like organ called an ovipositor to cut parallel slits into the bark of woody plants.
These cuts are made into young, tender branches, typically those about the diameter of a pencil (1/8 to 7/16 inches). The female deposits between 10 and 25 eggs inside each slit, creating a protected place for the next generation. A single female may create numerous cuts across various branches, potentially laying up to 600 eggs during her short lifespan.
The structural damage caused by these incisions disrupts the flow of nutrients and water to the tissue beyond the cut. This interference causes the tips of the affected branches to wilt, turn brown, and eventually die. This characteristic browning and drooping of branch tips is commonly referred to as “flagging.”
Mature trees are generally able to recover from flagging, as the damage is confined to the small, peripheral branch tips. However, young trees, new transplants, and thin-barked shrubs are far more vulnerable to permanent injury. Extensive flagging on a young tree can interfere with its growth or even cause it to be killed. The oviposition scars can also weaken the branch structure, making it susceptible to breaking or creating entry points for canker diseases.
Protecting Vulnerable Vegetation
Homeowners can take proactive steps to protect susceptible plants from the structural damage caused by oviposition. The most effective mitigation strategy involves creating a physical barrier to prevent females from accessing vulnerable branches. This protection is best achieved by covering young trees and shrubs with a fine mesh netting material.
The netting should have a mesh size no larger than one-quarter inch to effectively exclude adult insects. This covering should be applied as the first cicadas emerge and secured tightly around the trunk to close any gaps. It is also wise to postpone planting new trees or woody shrubs with a trunk diameter of less than two inches until after a major cicada emergence period has concluded. Applying insecticides is generally not a recommended or effective control method against swarms of adult cicadas.