ST. LOUIS – Cicadas are beginning to emerge in the eastern United States after spending the past 17 years underground.
“There are thousands of species of cicadas. And there’s only seven species of periodical cicadas. Four of them emerge every 13 years and three emerge every 17 years,” said Brett Seymoure, a postdoctoral fellow with Washington University.
This year, cicadas from Brood X, or ten, which last emerged in 2004, are emerging as far west as Illinois. Their mothers laid their eggs at the base of trees where hatched nymphs ate their way into the tissues of the tree. There they waited while feasting on sap.
“They count years based on actual sap nutrition status. So, a tree’s sap is going to change throughout the year based on the resources it’s eating. So, they can basically say okay it’s been one year since, now the sap has gotten worse and now it’s better,” Seymoure said.
When they finally come above ground, it’s mating time. Males try to attract females by making loud clicking sounds using a muscle on their abdomen.
“This courtship song — super loud. Incredibly loud. Orders of magnitude, 10 times louder than your loudest washing machine,” Seymoure said.
Cicadas are an important food source. That actually may be why they emerge only once as such a large group.
“One defense that works very well is just to make sure you’re with a bunch of other individuals and your chances of being eaten go way down.”
So, these loud but important insects have been underground for seventeen years. A lot has changed since then. Seymoure studies the effects of light pollution on animal behavior with the Living Earth Collaborative at Wash U. He says other insects have a chance to adapt to human impacts on the world.
“Certain insect species–for example, some moths–have evolved to stop flying to artificial lights at night,” Seymoure said.
But cicadas, which cue into changes in temperature and changes to the trees they feed on, don’t have multiple generations a year to evolve through.
“Cicadas that’s 17 years, that’s very very slow. That’s human generation time,” he said. “How are these insects going to keep up with the fast pace of global change due to humans? And we don’t know that yet.”