This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Every 13 or 17 years, swarms of cicadas emerge from the ground, their black bodies, orange-tinged wings and ruby-red eyes enveloping trees and forests. It is a biological marvel unique in the insect world, and when it happens, it is impossible not to notice.
But those mass emergences may be coming to an end. In a new study published in Ecology, biologists at the University of Iowa have concluded that periodical cicadas—species that emerge every 13 or 17 years—could be heading toward extinction. The main reason: the historical loss of old-growth forests, whose roots are the insects' sole, essential food source during their prolonged time underground.
Even when those old, intact forests are replaced by new trees, the insects are unable to adapt because they move very slowly into new habitats, the biologists found. It's a bit of a sad tale, admits Andrew Forbes, professor in the Department of Biology at Iowa and the study's corresponding author. "I think that cicadas are really cool because they have this amazing biology.
But that interesting biology has also doomed them," Forbes says. "Their viability is connected with human land use. Forests get cut down, and they regrow, but these animals are living underground for 17 years, and when you cut down the old trees, the cicadas lose their food source, they die out, and it might take them hundreds of years to get back." Periodical cicadas are found only in North America and are different from annual cicadas, which appear each year.
There are seven periodical cicada species, four with 13-year life cycles and three with 17-year cycles, all of which originated from a common ancestor nearly 4 million years ago. Each brood spends most of its life cycle underground, tracking seasons and years, before emerging synchronously and en masse in densities that can reach up to hundreds of thousands of insects per acre. They persist through sheer numbers.
Periodical cicadas have no known defenses against predators, making them easy pickings for birds and small mammals. Their overwhelming abundance is their evolutionary trick to survive. Forbes got interested in periodical cicadas as a graduate student.
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