ANDERSON — A natural phenomenon 17 years in the making will soon appear in Indiana.
Periodic cicadas known as Brood X, last seen in 2004, will emerge as soil temperatures reach 64 degrees at a depth of 8 inches, according to scientists. That will likely occur this month or next.
“Around the time that the irises start to bloom, the cicadas will start crawling out of the ground. It’s kind of like a scene from the night of the living dead,” said Cliff Sadof, a Purdue University professor who specializes in pest management.
As many as 1.5 million cicadas per acre will emerge and climb up tree trunks and posts to molt. Immediately after molting, they will be white in color and will unfurl their new wings as they wait for their new bodies to harden.
“Over time, the wings get harder, the body gets harder. It takes a couple hours,” Sadof said.
Males will fly into the treetops and start singing; females will respond with a clicking noise.
After they find each other and mate, the females will lay eggs in twigs about the width of a pencil, Sadof explained.
“They have a little saw-like egg-laying device, which we call an ovipositor,” he said. “They’ll lay an egg pretty much in any woody twig between 3/16ths and 7/16ths of an inch.”
After the eggs hatch, nymphs will fall from the treetops and burrow into the ground. There, the nymphs will feed on sap from tree roots.
Seventeen years later — in 2038 — they will emerge as adult cicadas, and the big, slow circle of their life cycle will start all over again.
WHY SO LONG?
Other varieties of cicada emerge annually. And another variety comes out every 13 years.
Why 13 or 17 years for periodic cicadas?
They survive by predator satiation. While birds and squirrels will feast, there will still be plenty left to create the next generation.
Cicadas “just overwhelm” predators, according to Sadof.
“When you come out once every 17 years, you don’t have a whole lot of predators building up waiting in the wings to eat you,” he said.
“About 98% of the cicada eggs never make it to adults,” he said. “They’ll die, the eggs may not hatch, the nymphs may not make it down to the roots. All kinds of things can happen, but the 2% that survive are quite successful.”
Each cicada produces several hundred eggs “so they can keep on repeating the cycle,” Sadof noted.
According to cicadamania.com, Indiana counties that hosted Brood X in 2004 include Brown, Clark, Clay, Bartholomew, Crawford, Daviess, Dearborn, Dubois, Fountain, Gibson, Greene, Jackson, Jefferson, Jennings, Lawrence, Martin, Monroe, Montgomery, Orange, Owen, Parke, Perry, Pike, Ripley, Spencer, Sullivan, Vanderburgh, Vigo and Warrick. Other counties might have hosted the brood in 2004, as well.
Periodic cicadas will appear only in areas where there were trees 17 years ago. An area planted since then or an area where trees were removed in the past 17 years won’t host a cicada coming-out party this time around.
The cicada emergence this spring will offer a citizen science opportunity. Hoosiers can contribute to the understanding of the distribution of Brood X across the state.
Purdue is running two projects through the iNaturalist app and website. One is for master gardeners tracking the emergence. The second is a bioblitz for everyone.
Elizabeth Barnes, exotic forest pest educator at Purdue, explains.
“We want people to go out during a specific week and find an area with cicadas, and then take pictures of any sort of organisms that they find, hopefully often including cicadas, and upload them onto our project on iNaturalist,” she said.
“That’s more about generally collecting biodiversity data and also to see if we can collect more information about where cicadas are distributed throughout Indiana,” Barnes added. “We have spotty records in some areas.”
Homeowners shouldn’t be worried about cicadas damaging mature trees, according to Sadof.
The twigs where cicadas lay their eggs will die, turn brown and eventually fall to the ground. While temporarily unsightly, the tree will recover.
The tree might even get a boost in growth the following year as the decaying cicada carcasses mulch and fertilize the ground at the base of the trees.
“You can hire an arborist or landscaper to come and clean up the deadwood after it starts to look brown. Or you can just wait until it falls off,” Sadof said. “Since it happens once every 17 years, try to put it in perspective.”
Younger trees can be protected by netting with a grid of less than a half-inch. But spraying insecticides should be avoided.
“In May, when you spray insecticides you kill all the predators of spider mites and other different kinds of insects,” Sadof cautioned. “You can wind up having more pest problems than you started out with by spraying early in the season.”