A cicada swarm is a large-scale, synchronized emergence of cicadas from underground. These events involve millions, potentially even trillions, of these stout-bodied insects appearing at once. Cicada swarms are natural biological phenomena, not an “invasion” or “apocalypse” as some might fear. They represent a distinct phase in the cicada life cycle.
Understanding Cicada Emergence
Cicada swarms are driven by the life cycles of periodical cicadas. These insects spend most of their lives, either 13 or 17 years depending on the species, underground as nymphs. During this subterranean phase, they feed on the xylem fluid from tree roots, growing from the size of a small ant to nearly adult size.
The synchronized emergence of these periodical cicadas is a remarkable adaptation. They emerge en masse to transform into adults, mate, and reproduce. This strategy, known as predator satiation, overwhelms predators with sheer numbers, ensuring that enough individuals survive to continue the species.
Environmental cues, soil temperature, trigger their emergence. When the soil at a depth of 8 to 18 inches reaches 64 degrees Fahrenheit (18 degrees Celsius), nymphs begin to dig their way to the surface. Male cicadas emerge a few days before females. Annual cicadas, in contrast, have shorter life cycles of two to five years, and their emergences are not synchronized, so some adults appear every summer.
Impact on Surroundings and Duration
The most noticeable impact of a cicada swarm is the loud noise. Male cicadas produce mating calls using tymbals on their abdomens. The sound can reach 90 to 100 decibels, comparable to a lawnmower or a jet engine at close range.
While their numbers and noise can be overwhelming, cicadas are harmless to humans and pets; they do not bite or sting and are not poisonous. They are distinct from locusts, as cicadas feed on tree sap and do not consume garden plants or crops. If a cicada lands on a person, it is usually accidental, as they are seeking trees for mating and egg-laying.
Female cicadas lay eggs in slits they create in the branches of woody plants. This egg-laying can cause young or newly planted trees and shrubs to experience “flagging,” where branch tips wilt, turn brown, and may break off. Mature, established trees are not significantly harmed and can recover from this natural pruning. The above-ground adult phase of a cicada swarm lasts four to six weeks, with the loudest chorusing occurring for three to four weeks.
Ecological Role
Cicada swarms play an important role in their ecosystems. Their emergence provides a temporary food source for a wide variety of wildlife. Birds, small mammals, reptiles, and even fish feast on the abundant cicadas, which can lead to a temporary increase in predator populations.
As nymphs tunnel through the soil, they naturally aerate the ground. This process improves soil structure, enhancing water infiltration and nutrient movement to plant roots.
After adult cicadas die, their decomposing bodies return organic matter and nutrients to the soil. This acts as a natural fertilizer, enriching the soil and supporting plant growth.