Cicadas are insects known for their distinctive sounds and periodic appearances. Their large-scale emergences often raise questions about their role in the ecosystem, particularly if they are an invasive species. This article clarifies the nature of cicadas and addresses this common misconception.
Understanding Cicadas
Cicadas are insects belonging to the order Hemiptera, characterized by their stout bodies, prominent eyes, and clear, membranous wings. There are over 3,000 species worldwide, with about 190 found in North America. These insects spend the majority of their lives underground as nymphs, feeding on the watery sap (xylem) from tree roots.
Cicadas are categorized into two types: annual and periodical. Annual cicadas have life cycles typically spanning 2 to 5 years, with some adults emerging every summer. Periodical cicadas, found exclusively in eastern North America, have synchronized life cycles of either 13 or 17 years, emerging en masse in specific locations. When soil temperatures reach around 64 degrees Fahrenheit, mature nymphs tunnel out, molt into winged adults, and begin their brief adult stage focused on mating and egg-laying.
Defining an Invasive Species
An invasive species is defined as non-native to a particular ecosystem, whose introduction causes or is likely to cause environmental or economic harm, or harm to human health. Not all non-native organisms are invasive; many agricultural crops, for example, are non-native but beneficial.
Invasive species can cause harm by leading to the extinction of native plants and animals, reducing biodiversity, and permanently altering habitats. They are typically introduced through human activities, often unintentionally, such as via ship ballast water. Therefore, mere presence or large numbers do not qualify a species as invasive; both non-nativeness and demonstrable harm are necessary criteria.
Cicadas: Native or Invasive?
Despite their sometimes overwhelming numbers and loud presence, cicadas are not an invasive species in North America. The large, noticeable emergences of cicadas, including both the annual and periodical types, involve species that are native to the North American ecosystem. Periodical cicadas, for example, are unique to eastern North America. Their long life cycles and synchronized emergences are a natural phenomenon that has evolved within these environments over millions of years.
Cicadas do not fit the definition of an invasive species because they are native to the regions where they emerge. They are an integrated part of the native food web and play a role in the ecosystem’s natural cycle. Their synchronized emergence is a defense mechanism, allowing them to overwhelm predators through sheer numbers, a phenomenon known as predator saturation.
Actual Impacts of Cicada Emergence
Cicada emergences, while sometimes startling due to their scale and noise, have specific and mostly temporary impacts on the environment. One observable impact is the damage female cicadas inflict when laying eggs, as they create small slits in tree twigs and branches. This can lead to “flagging,” where the tips of branches turn brown and die, particularly on young or newly planted trees. While mature, healthy trees generally tolerate this damage, it can be more significant for smaller, less established plants.
Beyond plant damage, the loud chorus produced by male cicadas, used to attract mates, is a prominent feature of their emergence. This noise, which can be as loud as a lawnmower or leaf blower, is a temporary nuisance during their brief adult lifespan. Cicadas also serve as an abundant food source for various wildlife, including birds and other animals, providing a temporary boost to predator populations. Their tunneling activities as nymphs contribute to soil aeration, and their decomposing bodies enrich the soil with nutrients, acting as a natural fertilizer.
Managing Cicada Nuisances
While cicadas are not considered harmful to the overall ecosystem, their emergence can pose a temporary nuisance, particularly for young trees and shrubs. Homeowners can take simple, practical steps to protect vulnerable plants. For instance, covering young trees with fine netting or cheesecloth provides a physical barrier against egg-laying females. The mesh should be fine enough to prevent cicadas from entering, typically with holes ΒΌ inch wide or less, and secured around the trunk.
Delaying the planting of new trees or shrubs until after the cicada emergence period is another effective strategy, especially if a significant brood is expected. Mature, established trees are generally resilient and do not require protection. Insecticides are typically not recommended for cicada control, as they are often ineffective against large populations and can harm beneficial insects.