Brood X is here at last.
Trillions of cicadas, underground for the last 17 years, are burrowing up through the soil and emerging in numerous eastern and midwestern states to transform, sing, and mate.
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Brood X (the X is for the Roman numeral 10) will shed their nymphal skins, sing their deafening songs and mate. Then they’ll die and it’s all over until 2038, when the next generation emerges from the ground.
After 17 years, their above-ground life cycle is surprisingly short, but productive. It typically goes something like this:
The cicadas start emerging in mass numbers when the soil temperature reaches 64 degrees Fahrenheit, usually on a day with a soaking rain that softens up the soil, explains Gene Kritsky, the dean of behavioral and natural sciences and professor of biology at Mount St. Joseph University in Cincinnati, Ohio.
Kritsky typically goes out after dark and watches as the cicada nymphs climb up a tree, or a brick wall, or a fence, locking their legs onto a vertical surface.
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“[T]he back of the cicada nymph splits and you see this white space appear, and eventually it gets a little wider, and then the head capsule splits on the top. And then the whole adult pulls itself out of the old nymphal skin, wriggles its abdomen free. And there you have it — it’s a separate adult now.”
“Then the back of the cicada nymph splits and you see this white space appear, and eventually it gets a little wider, and then the head capsule splits on the top,” Kritsky says. “And then the whole adult pulls itself out of the old nymphal skin, wriggles its abdomen free. And there you have it — it’s a separate adult now.”
At this point, the cicada has small, shriveled wings and it’s creamy white with red eyes and two black patches behind its head, Kritsky continues. For the next 30 to 40 minutes, it starts expanding its wings by pumping fluid through them. The wings grow bigger until finally they’re held in place, tent-like, over the back of the abdomen. It then takes another hour-and-a-half for the cicadas to turn dark, get an orange color to their wing veins and turn into the typical adult cicada.
“After they’ve transformed into the adult, they’re going to climb to the top of the trees for about five days,” Kritsky says. “It’s really strange because for the few days after they first started coming out, you don’t hear any calling. That doesn’t start till about five days later, after they’ve completed the hardening of their exoskeleton, and they’re ready to fly and sing.”
All the males gather in large numbers in trees and start singing — scientists call it a “chorusing center.” Females fly into a tree, and when a male sings, she responds by flicking her wings. If he hears that, he’ll walk closer and call again. She’ll flick her wings again and he’ll walk still closer. Eventually, they mate.
When mating is complete, the female will start laying her eggs within the next couple of days. She’ll lay 500 eggs in the terminal growth of tree branches, and then she and the male die. The eggs remain in the trees, just under the bark. Six to 10 weeks later, they’ll start hatching.
“The nymph wriggles its way free from the egg nest and then just drops to the ground, and they’re gone, and it’s almost instantaneous.”
“The nymph wriggles its way free from the egg nest and then just drops to the ground, and they’re gone, and it’s almost instantaneous,” Kritsky says. “They’ll feed on grassroots or other herbaceous roots for a few weeks, and then on New Year’s Day, they’ll be 8, 10, 12 inches below the surface, sucking on a tree root. And that’s where they’ll be for the next 17 years.”
Aside from the sheer number of cicadas that emerge, their most distinctive feature is the sound they make, which can be deafening.
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There are three different species of 17-year cicadas and each of their calls is different. Calls are made with a structure called the tymbal, a membranous structure just under the wings of the first abdominal segment. Inside the male cicada’s body, muscles attached to the tymbal contract, causing the ribs to buckle, which makes the sound. They do this 250 times a second.
The male’s abdomen is mostly a hollow airspace the helps the sound resonate. Females don’t have a tymbal, so they are silent except for the flicking of their wings. “Get them all together into one large group, and it’s almost like a surreal experience,” Kritsky says.
The largest species of cicada, Magicicada septendecim, sounds to Kritsky like “what a Foley artist [sound artist] would have used for the flying saucers in a 1950s science fiction movie.” The second, Magicicada Cassinii, produces a series of buzz and clicks. The third, septendecula, is the rarest — 5% or 10% of the group in some locations — and to Kritsky sounds like a rotary sprinkler head.
“[To] add a little more spice to [the cicada sound], make it about 96 decibels, which is on par with a rock concert. That’s the music of a cicada symphony.”
“And that’s what your full-fledged chorus would be,” Kritsky says. “Then to add a little more spice to it, make it about 96 decibels, which is on par with a rock concert. That’s the music of a cicada symphony.”
Cicadas do considerable good for the ecosystem in which they live, Kritsky adds. They don’t alter the ecosystem like beavers do, for example, but they’re good for its survival.
During the 17 years cicadas are underground, they are turning over soil and tunneling. When they emerge, they come out of holes about the diameter of a pinky finger, which provide natural aeration for the soil. And in the warm summer months, during a heavy rain, a lot of that water goes down those holes and helps water the trees.
The cicadas emergence is also “an opportunistic food pulse that’s just amazing,” Kritsky says.
“Raccoons, squirrels, birds of all kinds, thoroughly enjoy periodical cicadas. And some people might not think that having more rodents would be a good thing, but in natural areas, more rodents mean more food for owls and raptors. So it can help those populations increase for this year, which may help more offspring to go into the future.”
Finally, when all the cicadas die, the carcasses collect at the base of trees and start to rot. They “really stink to high heaven,” Kritsky says, but as they decay, the nutrients from the rotting cicadas go into the soil around the trees, helping the trees grow and helping the new generation of cicadas that will be feeding on those trees.
Kritsky encourages people to download an app he created called Cicada Safari, which helps scientists map Brood X’s locations. The app will let you know where cicadas have been in previous years, but it will also let you update the app with new locations.
“Already we’ve had cicadas emerge this year from areas where we did not expect them,” Kritsky notes.
“Go out there, find a cicada, photograph it from your app and submit it,” he urges. “The value of Cicada Safari is it is a citizen science project where there’s verification. We’re tickled with this. We’re expecting 90,000 to 100,000 photographs this year.”
This article is written by Adam Wernick based on an interview that aired on Living on Earth from PRX.