Periodical cicadas emerge in enormous, synchronized broods because appearing in large numbers can overwhelm predators: predators may eat many insects, but still leave enough cicadas to reproduce. Their 13- or 17-year life cycles also keep them underground for long periods; seasonal soil conditions help cue when mature nymphs surface.
Not every cicada follows this schedule
Periodical cicadas in the genus Magicicada are native to eastern North America. Depending on the species and brood, they spend 13 or 17 years developing underground before emerging as adults. Many other cicada species appear annually or follow different life cycles, so the famous long interval is not a rule for all cicadas. [1]
A synchronized swarm can overwhelm predators
Birds, mammals and other animals eat cicadas. If a brood emerged in small numbers over a long period, predators could consume a larger share of it. A mass emergence supplies so many insects at once that predators can become full while many cicadas remain to mate and lay eggs. Biologists call this predator satiation. [2]
The long cycle limits predictable overlap
Thirteen- and 17-year broods are difficult for predators with shorter generation times to track reliably. Their prime-numbered cycles also rarely synchronize with one another, although this is best treated as an evolutionary explanation supported by ecological reasoning rather than a simple proven purpose for every trait. Research has directly examined how predation and emergence timing affect survival. [3]
Weather cues the final emergence
After years underground, mature nymphs respond to seasonal environmental conditions, including warming soil, as they prepare to surface. Cicadas from a brood emerge within a seasonal window rather than reading a calendar. Their long underground development and the synchronized adult stage together create the dramatic “cicada year” people notice above ground.
Sources and evidence
- University of Maryland Extension — Cicadas in Maryland ↗
Describes 13- and 17-year periodical cicadas, broods and predator satiation.
- University of Connecticut — Periodical Cicada Information ↗
University resource on the synchronized emergence and predator-satiation hypothesis.
- Ecology — Emergence of 13-Year Periodical Cicadas: Phenology, Mortality, and Predator Satiation ↗
Field research testing the relationship between synchronized emergence, mortality and predator satiation.
Sources consulted: 14 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Initial publication; the summary distinguishes periodical cicadas from annual species and identifies predator satiation as an explanation supported by research.