Cicadas, their nostalgic hum that fills the warm evenings of spring and summer is just about as American as apple pie. In recently published research, UTC professor DeAnna Beasley and her colleagues got to know those symphonic (or annoying) performers and made some surprising discoveries.
Authors include DeAnna E Beasley, Clint A. Penick, Nana S. Boateng, Holly. L Menninger and Robert R. Dunn.
Their cicada of study, scientifically known as the Magicicada, is a genus of periodical cicadas that emerges from the earth every 13 to 17 years. They spend their long lives underground and break free en masse, as a brood of anywhere from 30,000 to 3.5 million. Every time they emerge, these cicadas are entering a brand-new world.
“I’ve been fascinated by periodical cicadas for many years. These are among the longest-live insects on the planet; the adults we studied were 17 years old,” Beasley says.
With the help of citizen scientists, researchers collected cicadas from North Carolina to Connecticut. They discovered that, in colder climates, the cicadas’ size was noticeably different in urban environments.
Scientists have known that the further north and the colder the climate, the smaller the insect. The idea is that, in warmer areas, insects tend to be larger because they have more time and energy to grow. In the scientific community, this pattern is known as the “converse Bergmann’s rule.”
But up north, urban cicadas weren’t following the norm.
People of all ages—including K-12 students participating in an online lesson titled What’s the Buzz: Citizen Science with Cicadas sponsored by online educational website, Student Discover— collected dead cicadas and shipped them to Beasley. Researchers then got to work measuring the bugs’ wings. Their focus wasn’t just on size, but developmental stability, too.
“So a way you can do that is you can measure differences in symmetry. Are they able to stick with the same plan and build an equal wing on each side?” Beasley says.
As measuring went on, patterns emerged. Most seemed pretty normal. In the South, urban cicadas weren’t any different from their rural counterparts. But in the North, cicadas from urban areas were much larger than their rural counterparts.
Although their study didn’t dig too deep into what was causing the differences, Beasley said she and her colleagues have a hunch or two. One is the “urban heat island” effect. Pavement in cities absorbs heat and raises temperatures, potentially leading to the larger growth, she explains. Other factors could be resource availability.
The differences in growth patterns open up conversations about how changing landscapes are impacting cicadas and other species.
“Two periodical cicada broods have gone extinct in the last century, including the Florida brood,” Beasley said. “As the United States’ East Coast becomes increasingly more urban, continued monitoring of urban cicadas will be important for understanding impacts on vulnerable populations.”