University of Iowa scientists warn that North America's periodical cicadas — which emerge every 13 or 17 years — are at risk when old-growth forests are cleared. Nymphs depend on the roots of mature, undisturbed trees, and mass emergences rely on very large, synchronized populations. Because cicadas recolonize new habitat extremely slowly, local populations can vanish for centuries, making protection of mature woods essential.
Study: 13- and 17-Year Periodical Cicadas Risk Local Extinction as Old-Growth Forests Disappear
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University of Iowa biologists warn that one of North America's most dramatic natural events — mass emergences of periodical cicadas every 13 or 17 years — may be slipping toward local extinction as old-growth forest habitat is lost.
Why Periodical Cicadas Are Vulnerable
Periodical cicadas spend the vast majority of their lives as nymphs underground, feeding on the roots of mature, undisturbed trees. There are seven species of these insects in North America: four with 13-year cycles and three with 17-year cycles. When entire broods emerge in synchrony, densities can reach into the hundreds of thousands per acre, a strategy that overwhelms predators and ensures enough survivors to reproduce.
What the Study Found
Researchers, led by Andrew Forbes of the University of Iowa, report in Ecology that removing or fragmenting old trees destroys the root resources cicada nymphs need. Because cicadas rely on predator satiation — emerging en masse so predators cannot consume them all — shrinking populations and habitat fragmentation undermine this survival strategy. Even when forests regrow, cicadas recolonize replacement habitat extremely slowly, meaning local recoveries can take centuries.
Andrew Forbes, corresponding author and professor of biology at the University of Iowa, said: 'I think that cicadas are really cool because they have this amazing biology. But that interesting biology has also doomed them.'
Real-World Observations and Consequences
Forbes' concern began in graduate school and was reinforced when an expected emergence near Iowa City produced far fewer cicadas than anticipated. That observation motivated the research and highlights how human land-use changes enacted over decades can erase a natural spectacle that communities have known for generations. Because cicadas spend nearly their entire lives underground, population losses may not be detected until a scheduled brood simply fails to appear.
Conservation Implications
The authors stress that protecting mature, undisturbed woodlands is critical. Planting young trees alone is not an immediate solution: while forest cover can return, cicadas' slow spread into new habitat means local populations may remain absent for hundreds of years. For homeowners, land managers and policymakers, preserving patches of older forest and avoiding unnecessary clearing can help maintain these iconic insect outbreaks.
Related research shows similar patterns elsewhere: iconic insect declines have been documented in parts of Costa Rica, and Yale researchers warn that broad butterfly losses could signal deeper ecological disruption. Taken together, these findings underscore that habitat loss can eliminate remarkable species and natural events long before the full scope of the damage is recognized.
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