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Cicadas are back, but climate change is disrupting their biological clock

Billions of cicadas are emerging in about 16 states in the Southeast and Midwest. Periodic cicadas used to emerge reliably every 13 or 17 years, depending on their brood. But in a warming world where spring conditions arrive earlier, climate change plays with bugs’ internal wake-ups.

Scientists believe that cicadas count years by changing fluid flow in tree roots, and when their emergence year arrives, they stay underground until soil temperatures reach 64 degrees Fahrenheit. Spring weather is now occurring earlier, with the season warming 2 degrees Fahrenheit in the United States since 1970, according to Climate Central, a nonprofit organization that studies climate change.

Spring comes earlier means cicadas too. Last month, the the return of cicadas has begun in Georgia nearly two weeks ahead of schedule before spreading north to the Chicago suburbs. The Southwest experienced the most significant spring warming, with areas of Nevada, Texas and Arizona exceeding 6 degrees Fahrenheit of spring warming since 1970, according to Climate Central.

“In 2021, they appeared 11 days, or almost two weeks, earlier,” said biologist Gene Kritsky, who has studied cicadas for decades. “This is true for Baltimore, for Washington, for Philadelphia, for Indianapolis.”

Cicada watchers were once able to predict their emergence as easily as astronomers could predict the appearance of cicadas. recent solar eclipse. But this has become more difficult as cicadas’ habits change as warm spring days occur more often.

Cicadas on a tree in Georgia
Brood XIX cicadas are seen on a tree in Angelville, Georgia, May 23, 2024.

ELIJAH NOUVELAGE/AFP via Getty Images


In 2007, a mid-winter heat wave in Ohio caused leaves on trees to grow prematurely, tricking cicadas into thinking an entire year had passed. Kritsky said this caused them to miscount the years, and when real spring arrived months later, they appeared a year earlier than expected.

“They had two fluid streams, so for them it was 17 years,” Kritsky explained. “They didn’t detect that it was just a few weeks. They just detected that the fluid stopped and then started again,” Kritsky said.

Once back in the world, they only live for a few weeks with one goal in mind: ensuring the survival of the species.

“They arrive in large numbers to overwhelm their predators. So the predators can eat all the cicadas they want, and there are still millions left to reproduce,” Kritsky said.

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