Jun. 10—What happens only five or six times a century and only once in a person's childhood?
The answer to that riddle can be found in the trees.
They're called Brood X periodic cicadas, and they're popping up by the millions here in the Midwest and along the East Coast.
And if you haven't heard or seen any yet in your area, experts say to just be patient.
A different brood
Step outside on a hot late-July day, and you've likely heard what some refer to as the sound of summer, the hum of cicadas in nearby treetops.
But there are actually over 3,000 different species of cicadas, according to Megan Abraham, entomologist and director of the Division of Entomology and Plant Pathology for the Indiana Department of Natural Resources, and they fall into two different categories.
"There are annual cicadas, and then there are the periodic cicadas," she said. "The annual ones obviously come out every year, but then you have others that appear every 13 years, and in this case with the Brood X cicadas, they are every 17 years. And Brood X, which refers to Brood 10, is the only 17-year periodical brood that we have here in Indiana."
They're easy to spot, too, Abraham added.
While annual cicadas are often green or yellow in color, Brood X periodic cicadas are the largest in the species, with black bodies and predominantly red eyes.
"They can look intimidating to those who have a phobia of insects," Abraham laughed, though she added that they are quite harmless.
And though they do arrive every 17 years, their history is somewhat clouded.
"I will say there's a good chance that they've been here a lot longer than we've been paying attention to," Abraham said. "... I would even guess that these guys have been around a lot longer than most of us have, but we just weren't around to see it."
But why do they only emerge every 17 years?
Experts note that it has a little to do with Darwinism.
Survival of the fittest
Mathias Ingle is an agriculture and natural resources educator for Howard County's Purdue Extension Office, and he said there are several theories as to why the Brood X cicada only emerges every 17 years.
"Nobody really knows for sure, I suppose," he said, "but one of the theories is that there are a lot more of them when they appear so that they can overrun the predators. That then pushes the species forward."
Because they're still insects, Brood X cicadas are often eaten by other animals, such as birds, turtles, rodents and snakes, as well as even domesticated animals, such as dogs and cats.
So in order to keep their populations high by only emerging every 17 years, Ingle said they can assure survival of the fittest.
"This way, they basically make sure they can go on and re-populate in the future," he said. "There are other broods throughout the country doing the same thing year in and year out, but they're just on a different time schedule."
Abraham agreed with Ingle, adding that when there is essentially more prey than predators, it's easier to avoid becoming extinct.
"They want the best chance possible to survive into the future," she said. "So if there are too many insects around for predators to eat all at once, then there's a good chance that some of them will get around to laying eggs and starting their progeny before they're fed upon. This is really the intent of periodical cicadas. ... But it's not their ultimate purpose."
Their purpose, Ingle and Abraham said, is to find a mate, breed and then essentially die.
The longest-living insect
The last time the majority of Brood X cicadas made their appearance in Indiana was in 2004.
Those eggs that were laid and left behind back then are the ones you now see today, Ingle and Abraham said, making Brood X cicadas the longest-living insects.
So what have the baby cicadas that were laid in 2004 been doing for the past 17 years?
They've been feeding on the chutes of tree roots, going through several different stages of molting — or shedding their exoskeletons — and just waiting for the opportunity to rise to the surface.
Then, once the soil temperature reaches a consistent 65 degrees, the babies begin to emerge.
"After they emerge, they'll go through another molting process," Ingle said. "Those shell casings on things like trees and on the ground are the biggest pieces of evidence that we know that they're around. After that final molting is when they'll go into what we typically think of with these cicadas, the red eyes and black bodies and tips on the wings. Then they make their way further into the trees to ultimately find partners to mate with."
And because of their short life spans above the surface, Brood X cicadas don't waste any time, Abraham noted.
"While they spend most of their lives below the surface, they're only here for about six weeks when they emerge," she said. "In that time, they're only looking to mate and lay eggs, so they really have a specific goal to accomplish before they die. ... So that loud sound you hear when they're around, that's a mating call only produced by the males.
"Males have a piece in their abdomen that's strummed tight like a drum," she added, "so they pull those muscles on either side of that drum-like part called a tymbal, and it reverberates within their hollow abdomen to make what sounds like a drum noise or perhaps what a lawnmower sounds like."
After mating, the females then create small slits in new growth on trees, Abraham continued, where they proceed to lay their eggs in amounts of up to 500 eggs apiece.
"Later in the year, we'll start seeing some evidence of where the females have laid those eggs," Abraham said. "They'll start browning early on the ends, and it'll look kind of like a sun-scorch or something on the outer edges of the trees because the new growths will start turning brown. But it's nothing to be worried about, and it should be fine the next year."
Once the mating process has ended and the eggs laid, the males and females eventually die off and fall to the ground.
The eggs also fall out and go underground, usually during the autumn months, Abraham added, where they'll emerge again in 2038.
But even though they're large and perhaps intimidating looking, both experts said Brood X cicadas are horrible flyers and completely harmless to humans and animals.
"They do have mouth parts that are similar to a true bug," Abraham said, "but they're not able to bite. And because they can't fly very well, they're pretty much fumbling around and landing on things, so perhaps they might run out in front of your car on the road or land on you while you're walking around. But they can't do any damage, and it's nothing to be worried about."
In fact, Brood X cicadas have great environmental benefits, Abraham explained.
Impacts on nature
"For the last 17 years, these insects have been feeding underground on the root stalk that has high levels of nutrients," Abraham said. "So when these guys mate, lay their eggs and then die off, their bodies provide a good flush of nutrients that will go back into the soil. It's almost like a fertilizer for the forest floor or wherever they may finally fall down.
"Then, think of all of these insects being eaten by songbirds or small rodent populations, especially in those forest areas," Abraham continued. "Anything that can easily eat an insect is finding these things this year. So there will be a higher population of songbirds and game birds out there in the coming years because of this year's influx of cicadas."
Which is why conservation of their habitats is so important, Ingle noted.
"If say you had a group of cicadas that came in and populated themselves or laid their eggs in the 'back 40' woods, and you go in and clear that area of woods to farm or make a house, you're basically wiping out that population there for good," he said. "There likely won't be any in that particular location going forward because you've taken away their main food supply. ... These really are just another one of God's creatures, and we should treat them as such."
But while other places around the state and country are seeing their fair share of Brood X cicadas — upward of 1.5 million per acre in some areas — Howard County hasn't reported anywhere close to those numbers.
In fact, Ingle hasn't seen or heard about any at all yet, and he has his own theory as to why that seems to be the case.
Playing the waiting game
"I know that here in the county, we have a lot of new construction, like subdivisions and such," Ingle said. "That could play into it some. But I also suspect maybe that they're where we haven't looked yet, either — in a place that we know has had an ample and steady food source for the past 17 years. Right now, we know they're out there. It's just a big game of 'Where's Waldo?' at the moment to find them."
Abraham agreed with Ingle, noting that she believes the cicadas in this part of north-central Indiana are likely to appear sometime in the next couple of weeks.
"We're just starting to get some reports from our citizen scientists of some patches of them in Tippecanoe County and up in Fort Wayne," she said. "And we're really seeing them in Indianapolis and in the southern counties of the state. So it's just a waiting game right now. ... These guys need well-established trees in order to make it, and we have a lot of those here in Indiana. So if you aren't seeing them in your neighborhood, you won't have to travel too far to find them."
And people are traveling here to see them, too — from states as far away as Florida, Minnesota and Iowa, Abraham noted — with their ears tuned into the Hoosier treetops and fascination spread across their faces.
Enjoying the moment
Ingle smiled and said he couldn't really remember 2004, the last time the Brood X cicadas appeared, though he said he would have been in college at the time.
The time before that, he was just 6 years old.
As for Abraham, she said she didn't live here in 2004, but her parents did.
And every time she'd call home, her parents would hold the phone up so she could hear the loud drumming noise that echoed through their yard.
Because at the end of the day, these Brood X cicadas are simply fascinating, the pair noted, and they should be celebrated as such.
"This is something that we just don't often see," Ingle said. "They come, are here for a short time, and then you don't see them again for 17 years. So really, it's pretty easy to forget the last time they were even here. But it connects people in a way because everyone that lives here when they (the cicadas) do come have that same shared experience. It's fascinating really."
"If you think about it, what did the world look like when they came back in 2004 or 1987 or 1970, and so forth? And what will the world look like in 2038 or 2055 or 2072? It's super interesting to think of when you look at it that way. So just enjoy it for what it is. They're going to be gone soon enough, and we'll have to wait an awful long time to see them again."