Periodical cicadas (Magicicada septendecim), the cousins of katydids and crickets, have a unique breeding schedule, and after 17 years of living underground, a large group of them are preparing to fill the skies along the U.S. East Coast, from North Carolina up to Connecticut.
Normally, periodic cicadas spend their lives in complete darkness underground, sucking the fluid out of the roots of trees and shrubs. At the end of their life, they emerge, breed, and almost instantly die, completing a lifecycle that humans have studied for centuries….
Cicadas are easy to anticipate because of their extremely consistent mating behavior. Every 13 or 17 years, depending on the population, species of periodic cicadas will emerge as part of a specific brood in order to look for a mate.
The group expected this spring, known as Brood 2, are the offspring of cicadas last seen in 1996. If they follow the same tracks as their parents, they’ll emerge in Connecticut, Maryland, North Carolina, New Jersey, New York, Pennsylvania, Virginia, and Washington, D.C.
The genetic mechanism that prompts periodical cicadas to emerge kicks in every 17 years (or every 13 years for other broods) when the ground warms up to 64°F (18°C).
Some researchers think the timing of a brood’s emergence is a defensive mechanism—appearing at infrequent intervals means that it’s harder for would-be predators like birds and squirrels to anticipate when the insects will be available to eat.
Others suggest that the 13- and 17-year cycles, prime numbers in mathematics, help cicadas avoid parasites. A 2004 study from the University of Campinas in Brazil suggested that a cicada with a 17-year cycle and a parasite with a two-year cycle, for example, would meet only twice each century.
But not all cicadas breed on this multiyear cycle. Some, like the tibicen cicadas, work on an annual rotation, leaving them more susceptible to predators like the cicada killer wasp (Sphecius speciosus).
The wasps know exactly when to expect the annual cicadas in late summer or early fall. The wasp lays its eggs on the cicadas, and the larvae slowly kill the cicada and feed off its carcass.