Why billions of cicadas wait over a decade to emerge in perfect unison

Nature · Published 30 September 2026 Swipe more like this →

In short: Periodical cicadas spend 13 or 17 years underground, feeding on tree roots in total darkness. When they finally surface, they arrive in numbers exceeding one trillion, creating a deafening, synchronized spectacle. This extreme strategy is not just a biological curiosity; it is a sophisticated evolutionary defense against predators.

The genus Magicicada consists of seven species native to the eastern and midwestern United States. Unlike annual cicadas, which appear every summer, these insects are developmentally synchronized within a region. They spend nearly their entire lives as nymphs, tunneling 5 to 61 centimeters deep to feed on the xylem sap of tree roots. This subterranean phase is remarkably long, lasting 13 or 17 years, with the difference in cycle length attributed to the time required for the second instar to reach maturity.

The mechanism behind this precise timing remains a subject of study. Evidence suggests nymphs track the passage of years by monitoring seasonal changes in the xylem fluid of their host trees. In one experiment, researchers induced trees to drop and regrow leaves twice in a single calendar year; cicadas feeding on these trees emerged a year early, suggesting they rely on these physiological cues to count the seasons. Once the soil reaches a critical temperature, the nymphs emerge, shed their exoskeletons, and spend a fleeting three to four weeks as adults.

This emergence is a masterclass in predator satiation. By appearing in such overwhelming numbers—as seen in 2024 when Brood XIII and Brood XIX emerged simultaneously for the first time since 1803—the cicadas ensure that even if predators like birds, fish, and mammals gorge themselves, enough individuals survive to mate. The females then use their ovipositors to deposit 400 to 600 eggs into tree twigs. After hatching, the young drop to the ground to begin the cycle anew. This long, synchronized life cycle may also help them avoid specialized predators, such as parasitic wasps, that cannot easily adapt to such infrequent, massive pulses of prey.

While often mistaken for locusts, these insects are harmless to humans and do not bite or sting. However, their sheer numbers can cause damage to young trees, as the egg-laying process can cause branches to die. Despite this, most mature trees survive the metabolic drain of the nymphs, as the insects feed very slowly over their many years underground. This phenomenon, known as mast seeding in plants, is mirrored here in the insect world, proving that sometimes the best way to survive is to simply be too numerous to be stopped.

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