With spring in full swing, a subterranean clock is ticking in more than a dozen states. Once the soil in those places reaches 64 degrees Fahrenheit, billions of periodical cicadas will emerge to kick off their adulthood in the world above.
If you live in their path, you can expect to see a staggering number of these bugs dominating your local landscape — and loudly buzzing — between May and June. In warmer locations, some cicadas may have hit the scene as early as April.
READ MORE: Trillions of underground wonders to emerge in ‘cicada-geddon’, largest in centuries
These insects spend the majority of their lives underground, feeding off of tree roots. But every 13 or 17 years, different broods – groups of cicadas that debut at the same time – leave their underground lairs to mate.
2024 offers a rare entomological treat: Two different broods will emerge at the same time across different ranges of the country. The Great Southern Brood, or Brood XIX, will extend across Alabama, Arkansas, Georgia, Illinois, Indiana, Kentucky, Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee and Virginia, according to Illinois Extension. The Northern Illinois Brood, or Brood XIII, is expected to cover that region, plus parts of neighboring Wisconsin, Iowa, Michigan and Indiana.
Animation by Megan McGrew/PBS NewsHour
Two different broods don’t often emerge simultaneously — these particular 13- and 17-year cicada broods only sync up once every 221 years. They last emerged together in 1803, and their next double-emergence is predicted in 2245, said Kacie Athey, an assistant professor and extension specialist at the University of Illinois Urbana-Champaign.
Periodical cicadas serve several ecological purposes, like providing an ample food source for predators and decomposing into valuable soil nutrients at the end of their life cycle. But they can also pose a threat to saplings.
For people who work at tree nurseries, this year’s emergence might feel like a looming “cicada-geddon.” But one researcher is using the event as a unique opportunity to dabble in experimental cicada control methods that could one day benefit growers.
An experiment in cicada elimination
After mating, female cicadas use an organ called an ovipositor to saw into tree branches and lay hundreds of eggs inside the wood. This process doesn’t significantly affect mature trees, but it can weaken young tree branches, eventually causing some leaves to wilt and turn brown in a process called “flagging,” said Douglas Airhart, a professor of horticulture at Tennessee Tech University.
Sometimes, damaged tree parts can even break off when disturbed, which is bad news for a nursery where business revolves around growing, selling and transporting healthy, quality trees.
This year, Airhart is spearheading research to see whether various biopesticides — which are derived from sources like minerals or living organisms rather than something like petroleum — may be suited to killing adult cicadas, or prevent them from laying eggs. He’s also trying out a colorant and a scent that could repel them.
To test the biopesticides, Airhart’s team will cover dozens of potted oak saplings in netting, trapping adult cicadas underneath so they can’t escape when the materials are applied.
FILE PHOTO: A cicada from Brood X clings to a flower after emerging from its 17 years underground in Falls Church, Virginia, U.S., May 17, 2021. File photo by Kevin Lamarque/Reuters
The second part of their experiment will involve spraying some field-grown trees with a red colorant or the scent of a sweetgum tree, while leaving others alone as controls, to test whether those additions potentially repel cicadas. Other trees will be covered in netting, an expensive option that’s for now the only sure-fire way to keep cicadas at bay.
Airhart got the idea for the colorant from a Kentucky nursery where workers observed that certain trees with red or purple leaves appeared to fare better after periodical cicadas emerged compared to their greener counterparts. He chose the sweetgum scent as a “shot in the dark” test because he previously observed that these trees were notably unaffected by the insects.
“When I saw absolutely no damage on sweetgum trees, I said, ‘OK, why?’ Well, it’s either the way the bark is, which we can’t change, or it’s because the way it stinks, which we can test,” he said. “It’s almost a laughing matter. But if it works, it won’t be a laughing matter.”
Why entomologists encourage you to embrace cicadas
Despite the trouble periodical cicadas can cause for younger trees – and feelings of ick their massive numbers might stir in humans – they are generally harmless, and entomologists will tell you they embody a cool biological phenomenon.
That’s because these particular cicadas are quite literally a strange breed. Although different cicada species are distributed across the world, periodical ones only exist in the United States. They’ve also managed to thwart predators that may have otherwise evolved to hunt them due to their prime-numbered life cycles, which Athey noted no other animal has evolved to sync up with.
So, insectophobia aside, try not to panic when you do come across them, or if your dog chomps on a few of them during a walk, Athey said. Her advice is to lean in when these bugs come out, and make an effort to “appreciate some of the weirdness that’s around you.”
