Cicadas are large, noisy insects that spend most of their lives underground, emerging only for a brief, loud period of mating. Their sudden, overwhelming appearance and deafening chorus often cause public alarm, leading many to question if they are pests requiring eradication. Before reaching for a solution, it is important to understand the actual risks these insects pose versus the benefits they provide to the local environment. This analysis explains the ecological role of cicadas and offers a balanced perspective on managing their seasonal presence.
Are Cicadas Harmful Pests?
The primary damage caused by cicadas relates to the female’s egg-laying process, known as oviposition. The female uses a specialized, saw-like organ to slice small longitudinal slits into the bark of slender, pencil-sized branches, typically between one-eighth and one-half inch in diameter. She deposits batches of 10 to 25 eggs into these cuts, with a single female potentially laying over 500 eggs. This physical injury interrupts the flow of nutrients and water, causing the tip of the twig to brown, wilt, and die.
This dieback is commonly referred to as “flagging” and is the most visible sign of a cicada emergence. For mature, healthy trees, this loss of peripheral twigs is similar to natural pruning and rarely causes lasting harm. However, young trees, newly planted saplings, or stressed shrubs with a high proportion of small-diameter branches can suffer significant damage, sometimes leading to stunted growth or even death. The mass emergence also creates a nuisance, covering surfaces with discarded nymphal skins and producing a mating call that can exceed 90 decibels.
The Ecological Importance of Cicadas
Despite the temporary nuisance and localized damage, cicadas serve several crucial functions within the ecosystem. Their long underground life stage, which can last over a decade, prepares the soil for their mass emergence. As nymphs burrow to the surface, they create an extensive network of tunnels that effectively aerates the soil. This natural tillage improves water infiltration and root growth for surrounding plants, enhancing the overall health of the forest and landscape.
The massive, synchronized emergence of periodical cicadas acts as a temporary, high-protein food source for a wide variety of predators. This strategy, called predator saturation, ensures that enough cicadas survive to mate and perpetuate their species. Once the adults die after their short surface life, their bodies decompose, returning significant organic matter and a substantial nutrient boost of nitrogen to the soil.
Non-Lethal Management and Tree Protection
Since the damage is primarily focused on young or vulnerable plants, non-lethal, preventative measures are the most responsible way to manage a cicada emergence. The most effective defense for protecting small trees and shrubs is physical exclusion using fine netting. Netting must have a mesh size of one-quarter inch or less to prevent the large-bodied females from accessing the branches for oviposition.
The netting should be placed over the entire canopy and securely tied at the base of the trunk before the insects emerge, typically in early May. Keeping the netting in place for the duration of the adult cycle, approximately six weeks, provides complete protection until the insects die off. A simple preventative action is to delay the planting of any new trees or shrubs until the year after a major periodical cicada emergence is expected.
Chemical pesticides are not recommended for cicada control because they are ineffective against the sheer numbers of a mass emergence and can harm beneficial insects and wildlife. Furthermore, the insects are not actively feeding on leaves, making broad-spectrum spraying an unnecessary environmental risk.
Context: Understanding Periodical vs. Annual Cicadas
The urgency of the question depends heavily on the specific type of insect present. Annual, or Dog-day, cicadas emerge every year during the summer months, but their emergence is staggered. These insects are larger and fewer in number, and the minimal damage they cause to trees is rarely noticed.
The insects responsible for the mass swarms and widespread concern are the periodical cicadas, which emerge simultaneously in enormous numbers every 13 or 17 years. These periodical species are smaller and are distinguished by their bright red eyes and black bodies. Understanding which type is emerging is the first step in assessing the situation, as only the massive, synchronized appearance of the periodical broods poses a risk to young trees.