Cicadas are often mistaken for garden pests that chew leaves and destroy flowers. These insects do not possess the chewing mouthparts necessary to consume foliage, fruits, or vegetables like a beetle or a caterpillar. Cicadas, especially the periodical and annual species commonly found in North America, cause garden damage not through consumption but through a reproductive behavior that involves mechanical injury to woody plants. The physical damage they inflict can be significant, particularly to young trees and shrubs.
What Cicadas Actually Consume
Cicadas are specialized fluid feeders, relying entirely on plant sap for their nutrition. Both nymphs and adults feed by using needle-like mouthparts to pierce plant tissue and drink the internal fluids. This places them in the order Hemiptera, or “true bugs,” which includes other sap-sucking insects. Adults specifically target the xylem, the vascular tissue responsible for transporting water and dissolved mineral nutrients.
Adult cicadas feed on the xylem sap found in the young twigs of trees and woody shrubs. Xylem sap is highly diluted and nutrient-poor, requiring cicadas to consume a large volume to obtain energy, which is why they excrete fluid in constant streams. Nymphs spend years underground, feeding on xylem sap from plant roots. This subterranean feeding is rarely noticed and seldom causes harm to mature, established trees.
Oviposition: The Primary Threat to Plants
The most substantial and visible harm cicadas inflict on gardens comes from the female’s egg-laying process (oviposition). Female cicadas use a sharp, spade-like organ called an ovipositor to slice into the bark and wood of small branches. They create a series of narrow slits along the length of a twig, depositing between 20 and 30 eggs in each cut. This physical wounding disrupts the flow of water and nutrients within the branch, severely weakening it.
The classic visual symptom of this damage is known as “flagging,” where the leaves on the branch tips beyond the egg-laying site turn brown, wilt, and die. While mature trees can usually tolerate this natural pruning event, young trees and shrubs are particularly vulnerable. Branches about 5 to 10 millimeters in diameter, roughly the thickness of a pencil, are most frequently targeted. For newly planted trees or saplings, extensive flagging can lead to breakage, growth loss, or even the death of the entire plant.
Practical Steps for Garden Protection
Gardeners can take specific actions to protect their most vulnerable woody plants during a cicada emergence. The most effective strategy is the use of physical exclusion barriers, as insecticides are generally ineffective. Young trees, especially fruit trees, new shade trees, and ornamental shrubs, should be covered completely with fine mesh netting. The netting openings must be a half-inch (about 1 centimeter) or smaller to prevent adult females from reaching the branches to lay eggs.
The netting should be secured tightly around the trunk at the bottom to prevent insects from crawling up and should remain in place for the duration of the emergence period, typically four to six weeks. Another preventative measure is to delay the planting of new, vulnerable stock until the local cicada season has passed. After the cicadas are gone, damaged branches should be pruned back to a healthy bud or branch junction to promote recovery and new growth.