University of Iowa biologists are warning that one of North America's strangest and most spectacular natural events could be inching toward an end, as periodical cicadas — the insects that emerge in deafening waves across forests every 13 or 17 years — may disappear with the long-term destruction of old-growth habitat.
Here's what to know
According to a study in Ecology and a news release, scientists think periodical cicadas may be approaching extinction. The danger comes during the many years they spend below ground. Throughout that stage of life, periodical cicadas depend on the roots of old, undisturbed forests for nourishment.
Andrew Forbes, the study's corresponding author and a professor in the Department of Biology at the University of Iowa, said the traits that make these insects so unusual are also what leave them exposed. "I think that cicadas are really cool because they have this amazing biology. But that interesting biology has also doomed them," Forbes said.
Only North America has periodical cicadas, which are distinct from annual cicadas. There are seven species — four with 13-year cycles and three with 17-year cycles — and when a brood emerges in sync, densities can climb into hundreds of thousands per acre.
More background
Their survival strategy depends on abundance. Researchers said these insects have no known way to defend themselves from predators, leaving them vulnerable to birds and small mammals.
Instead, they make it by emerging together in such immense numbers that enough remain alive to reproduce. That approach fails when forests are removed.
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Forbes said that when old trees are lost, so are the root systems the cicadas rely on during their years underground. Forests may grow back, but the insects move into replacement habitat so slowly that recovery can take hundreds of years.
Forbes' fascination with the question was both academic and personal. He became interested in periodical cicadas in graduate school, and years later he looked for an expected emergence around Iowa City only to find little.
It reflects how human land use can wipe out a natural phenomenon that communities have experienced for generations.
What can be done?
The findings suggest that protecting old-growth forests is critical. Because periodical cicadas spend nearly all their lives underground, the damage may not be obvious until an expected brood simply does not appear.
Planting new trees is not an immediate solution. Forest cover may return over time, but the insects' extremely slow spread into new habitat means recovery can lag far behind loss. Once a local population disappears, bringing it back is no simple task.
For communities, landowners, and policymakers, that raises the stakes for preserving mature woods and avoiding unnecessary clearing.
Where can I learn more?
As forests weaken and stable habitat disappears, species can decline fast — whether the threat is tree loss, vanishing insects, or the slow work of rebuilding biodiversity.
• In Costa Rica, iconic insect species are disappearing, alarming communities and ecologists alike.
• At Yale, scientists say broad butterfly losses could signal deeper ecological disruption.
Each of these stories shows that habitat loss can wipe out remarkable species long before most people realize what's happening. They also make clear why early action matters.
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