This year, 2021, a natural phenomenon will occur that you can either marvel at or be scared of. It’s the return of the 17-year cicadas. This insect is commonly known as the 17- year locust but they aren’t even related to the locust. It’s thought that they received that misnomer because they were associated with the plague of locusts in the Bible.
Even the term 17-year cicada is incorrect, according to Michael Raupp, PhD, professor emeritus in the Department of Entomology at the University of Maryland. In a recent magazine article, Dr. Raupp refers to them as periodic cicadas because some take only 13 years to mature. He also notes there are more than one species of this insect. There are four species of 13-year cicadas and three species of 17-year cicadas.
When we talk of them coming, that won’t be from afar like the birds in Alfred Hitchcock’s movie. In fact, if you didn’t have any in 2004 or 2008, you probably won’t have them now. They don’t go away for all those years. They’re living below the ground at the base of the tree(s) they occupied on their last visit.
For 13 or 17 years the immature nymphs live up to a foot below ground, feeding on plant roots. They go through five growth spurts, or instars. At the end of the fifth instar, they come to the surface, shed their exoskeleton and expand their wings. When their new adult exoskeleton hardens, thousands, even millions, of periodic cicadas take off all at once.
Dr. Raupp believes this swarming is for survival. Many predators like to feast on the periodic cicadas. (Some humans like them, too.) Emerging in huge swarms assures that, while many will fall prey to their hungry predators, they will overwhelm the enemy and a sufficient number will survive to reproduce.
If you’ve ever experienced periodic cicadas, you’re familiar with the din that comes forth from the trees hosting them. That noise is mating calls from the males wooing the females with their earsplitting choruses.
The females have a sharp appendage, called an ovipositor, with which they slit tender young twigs high in the crown of the tree, and deposit 20 to 30 eggs in each slit. Dr. Raupp says each female can lay up to 600 eggs. The slits in the twigs cause the tips of the branches to die.
Dr. Raupp cited research in which some trees were treated with chemicals and others with netting of various densities. The bottom line was that the only effective control was one centimeter netting. This is impractical for large shade trees, but those trees are big enough to survive. We may have to prune the dead branches, however. Small, young trees and fruit trees should be covered in netting to protect them. A periodic cicada infestation can cause significant damage to these trees.
All of this drama takes place in the spring, beginning in mid-May, and lasting until late June. After the nymphs hatch, they drop down to the ground and begin their subterranean life, until it’s time to emerge again in 2038. Reading this story almost makes you want to watch the movie (or musical play) Brigadoon, in which a Scottish village is visible for only one day every hundred years.