Brood XIX Cicadas Are Preparing to Make the Ascent of a Lifetime

The periodic cicadas that will surface in the Triangle in coming weeks have spent 13 years underground. In wooded areas and around bodies of water, we might see (and hear) up to a million an acre, according to Clyde Sorenson, a professor of entomology and plant pathology at NC State University.

Ahead of the upcoming emergence, the INDY spoke with Sorenson to learn more.

INDY: Talk to me about this year’s cicada season. What makes it so special?

SORENSON: Any time we have our local group of periodic cicadas emerge it’s a special thing. There are two different kinds of periodic cicadas: 17-year broods and 13-year broods. This only happens in eastern North America and nowhere else in the world. Our local brood is Brood XIX of the 13-year cicadas, and it’s the largest brood in the country. So it’s always cool.

But this year, it’s a little cooler because—even though it won’t have any impact on us here in North Carolina—this brood is co-emerging with a brood of 17-year cicadas, which is located largely in Illinois and surrounding areas.

When’s the last time that the two broods emerged at the same time?

1803. Thomas Jefferson was president.

Wow. OK. So you said that in the Triangle, we won’t be affected by the double brood, but the 13-year cicadas will still be something to behold. What should we expect to see, and when?

Many people are going to have them in their yards, if they have wooded yards. If folks want to go see them, there should be good numbers of them at Lake Crabtree Park, around Falls Reservoir at Falls Lake State Park, around Jordan Lake, and all around in Orange County and Chatham County. In Raleigh, they’re going to be mostly on the north and west sides of town. They will extend in patches all the way north of Rocky Mount. If you’re in an area where they are, you could experience as many as many as 1 million per acre. They’ll be coming up within the next couple of weeks. In 2011, they started coming up in late April, peaked in the first 10 days of May, and by the first week of June, they were pretty much gone. That could be shifted a week or more either way this year depending on how the rest of the spring runs and what the temperatures look like.

How do the 13-year cicadas impact local ecosystems?

It’s important to remember that they’re native animals that have been here for hundreds of thousands, if not millions, of years. So they have some impacts, but those impacts over the grand scheme of things are pretty ephemeral.

Our brood spends 13 years in soil feeding on tree roots. There’s some evidence that the year before they emerge, they depress the growth of the trees they’re feeding on because there’s simply so many of them. But then they come up, they mate, they lay eggs, and they die—and after that, there’s this large pulse of nutrition that goes back into the soil that those same trees can harness. There’s some evidence that the year after they come up, the trees grow more. So from the perspective of the trees, it’s probably pretty much a wash.

As far as other animals are concerned, everybody will eat them until they get sick of eating them. They come up in such huge numbers that the local predators simply can’t make much of a dent. But again, there’s this pulse of nutrition. There’s evidence that when they come up, some bird species are more productive in terms of nesting success because there’s all this protein sitting around waiting to be picked off.

They don’t cause any lasting harm to anything in the system. I would ask people to regard them as just a really spectacularly cool phenomenon that they only get to see every 13 years.

Could climate change have an impact on the cycles of periodic cicadas?

That’s a legitimate question that is receiving a fair amount of attention. Thirteen and 17 are both prime numbers—there are lots of interesting theories about why that is—but there is some evidence that as it gets warmer, the clocks are gonna get messed up, particularly for 13-year species, and they may shift to a shorter prime number emergence.

The other problem with climate change, of course, is that when climate changes, habitats change. These are insects that evolved in hardwood forests, and if something happens to those hardwood forests due to climate change, then that habitat is gonna contract. Development and land conversion have already pushed them back from where they were 500 years ago, before European colonization. And our activities continue to put pressure of that sort on them. They’re certainly not in any danger of going extinct in the next little while, but our activities could have a profound effect on how this looks in decades or maybe 100 years.

What are some of the theories around the cicadas’ prime number life cycles?

People have been puzzling over this observation since it was recognized. It’s pretty striking. One theory is that they’re deploying a strategy called predator satiation, where you come out in huge numbers all at once and there’s simply too many of y’all for any one individual to have a high risk of being eaten. If you’ve got a prime number development time, then that makes it very difficult for predators to synchronize with you.

The other idea is that they have prime number broods to maintain species distinctions and range distinctions. There’s some weird math that goes into it that, quite frankly, I don’t understand. I’m a naturalist. But in general, evolving toward a prime number tends to maintain the integrity of a particular brood and keeps it distinct from adjacent broods.

Because this is a phenomenon that only happens every 13 or 17 years at one site, it’s really difficult to understand what’s going on. If somebody like me is trying to study this, you only get to see it four or five times in your life and then your ticket’s punched.

Do you have big plans for the upcoming emergence?

I’m anxiously looking forward to them. I’m gonna organize some field trips for some of my students. It’s a phenomenon I think everybody ought to try and experience because it is so unique. The behaviors are really cool. When they come up, contrary to the annual cicadas—the dog-day cicadas that come up every year—these guys are completely unaware. They don’t care if you pick them up. They don’t mind it a bit. So you get an opportunity to observe him.

They’re beautiful animals. They sing otherworldly songs. The tredecim, in particular, has a song that sounds more like a spaceship than it does an insect. It’s just impressive to see, you know, thousands and thousands of one insect on a tree, yelling their little heads off from the canopy.

Between this and the eclipse, April is turning out to be quite the month for rare natural phenomena.

Yeah. The good thing about this one is it lasts a whole lot longer than two and a half minutes.

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