A periodical cicada — a member of Brood X — clings to a plant in May 2021 in Takoma Park, Maryland. Cicadas are divided into groups called broods based upon when they emerge.
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In a matter of months, they will dig their way out from underground, red eyes shining, deafening song filling the air. It will be a confluence of creatures the likes of which hasn’t been seen in the United Statessince Thomas Jefferson was president — and won’t happen again until 2245. It’s a rare emergence of insects some are referring to as cicadapocalypse.
Billions of cicadas are expected to surface this spring as two different broods — one that appears every 13 years, and another every 17 years — emerge simultaneously. The 13-year group, known as Brood XIX, or the Great Southern Brood, is the largest periodical cicada brood, stretching across the southeastern United States. The Northern Illinois Brood, or Brood XIII, emerges every 17 years.
“It’s rare that we see this size of double brood emergence,” said Dr. Jonathan Larson, an extension entomologist and assistant professor at the University of Kentucky. “We’re talking about an absolute oddity of nature, one of America’s coolest insects.”
Though the idea of a cicadapocalypse may seem foreboding, experts predict that the two broods won’t overlap significantly, and the bugs themselves, while loud and numerous, are harmless. Here’s what you need to know going into cicada season.
What to know about cicada broods
This spring’s bugs are part of a genus, or group, of cicadas in the eastern US known as the Magicicada, or periodical cicadas. Three species emerge on a 17-year cycle, and four species are on a 13-year cycle. (Scientists have long debated the significance of these numbers, which are both prime — some researchers have suggested that emerging on these prime-numbered years makes the periodical cicadas less likely to be killed by predators that have 2- or 3-year life cycles, but the jury’s still out.)
The pattern periodical species follow is different from that of “annual” cicadas, which don’t actually have an annual life cycle, even though you can see them every summer in much of the United States. The nymphs, or babies, of annual cicadas spend two to five years underground, slowly growing, until they’re ready to emerge. There are just so many overlapping generations that there appears to be a steady stream of these cicadas every year.
It’s easy to tell annual and periodical cicadas apart. Annuals tend to emerge later in the year than periodicals. For instance, the “dog day” annual cicadas in the genus Neotibicen tend to show up in the dog days of summer, around August, whereas the periodicals make their appearance in the spring. While there are numerous species of annual cicadas, many of them are large and greenish. Periodical cicadas are smaller and mostly black, with bright red eyes and orange-tinged wings and legs.
Cicadas are divided into groups called broods based upon when they emerge. A brood can contain cicadas from multiple species. As long as they’re adults in the same 13- or 17-year cycle at the same time, they count as members of the same brood.
Brood X cicadas appear in Indianapolis in 2021. Billions of cicadas are expected this spring as two different broods — Broods XIX and XIII — emerge simultaneously.
When and where will the cicadas emerge?
This spring’s periodical cicadas will make their appearance when the soil temperature 8 inches deep reaches 64 degrees Fahrenheit (about 18 degrees Celsius). It will likely happen sometime in mid-May. The individual bugs’ adult life cycles are just a few weeks, but their emergence will be staggered, so there will be about six weeks of cicadas.
That month-and-a-half period will be jam-packed with loud singing, mating and then dying, like “the most macabre Mardi Gras that you’ve ever seen,” Larson said.
Parts of the Midwest and Southeast are due for cicadas this spring. Northern Illinois, along with southern Wisconsin, eastern Iowa and northwest Indiana are likely to see bugs from Brood XIII; central and southern Illinois, most of Missouri and scattered areas of Kentucky, Tennessee, Virginia, Maryland, North Carolina, South Carolina, Georgia, Alabama, Mississippi, Louisiana and Arkansas are due to get Brood XIX bugs.
There are some areas of central Illinois where the two broods’ geographic ranges have historically been close to each other and could potentially overlap. However, predictions of a cicadapocalypse — in which Brood XIII and Brood XIX show up at the same place at the same time — are probably an exaggeration.
“We’re not even sure that they’re really going to overlap,” said Dr. Chris Simon, a professor of ecology and evolutionary biology at the University of Connecticut. Her research group at the university maintains a website of cicada information, which includes maps showing where the broods have historically emerged.
A Brood X cicada takes flight among the treetops in June 2021 in Columbia, Maryland. Broods XIX and XIII haven't been aboveground at the same time since 1803.
The double emergence of Broods XIX and XIII is rare, occurring every 221 years (when the 13-year and 17-year cicadas overlap, as 13 times 17 is 221). These two broods haven’t been aboveground at the same time since 1803, and after this year, they won’t be reunited until 2245.
However, the co-occurrence of different cicada broods, somewhere in the United States, isn’t quite as rare. It last happened in 2015; it’ll happen again in 2037.
Preparing for cicadas
Even though a major overlap of the two cicada broods is unlikely, only getting one brood in an area still means countless bugs.
“You should expect lots and lots of cicada exoskeletons to be covering your trees and shrubs. You should expect to hear lots and lots of noise,” Larson said. The insects are likeliest to be in wooded areas near water, he added.
While the sheer volume of insects, along with their distinctive jackhammer-loud sounds and bright red eyes, might give some people pause, Larson notes that cicadas are harmless. They don’t pose a risk to garden plants. However, if you have young trees, cicadas could potentially damage them when the insects cut into branches to lay their eggs. You can mitigate this harm by covering the trees with cicada nets.
Cicadas won’t bite or sting you or your pets. If your dog eats a cicada or two, he said, the animal will be just fine.
Dogs aren’t the only ones tempted to nosh on cicadas; people have eaten them for thousands of years. “They have kind of a natural, sweet nut flavor,” Larson said. (If you’re allergic to shellfish though, you should avoid eating cicadas— a protein in shellfish that’s tied to allergies is also present in many insects.)
Cicadas are loud and numerous come spring, but they're harmless. They won't bite you or sting your pets.
If you live in an area with cicadas making an appearance this spring, you can download community science apps to help researchers studying these bugs.
“The main thing we want people to know is that they should download the Cicada Safari app, which is free on the web, and all they have to do is photograph whatever cicadas they see,” Simon said. Those photographs are sent to scientists, who then map where and when the cicadas are emerging: information vital for scientists studying how climate change affects cicadas and predicting future cicada activity.
Beyond the bigger scientific story of cicadas, Larson said he hopes people will embrace cicada spring simply because it’s a rare chance to see some of the world’s most unusual bug behavior.
“These are some of the coolest insects in America,” Larson said. “I really hope that people will appreciate this for what it is: this unique natural phenomenon that you don’t get anywhere else. It’s beautiful.”
Kate Golembiewski is a freelance science writer based in Chicago who’s especially interested in zoology, thermodynamics and death.
Insights, advice, suggestions, feedback and comments from experts
Cicadas and Their Emergence Patterns
Cicadas are insects that belong to the genus Magicicada, also known as periodical cicadas. They are divided into different broods based on when they emerge from the ground. The broods can contain cicadas from multiple species, as long as they are adults in the same 13- or 17-year cycle at the same time [[1]].
The emergence patterns of periodical cicadas are different from those of "annual" cicadas. Annual cicadas do not actually have an annual life cycle, but they can be seen every summer in many parts of the United States. The nymphs, or babies, of annual cicadas spend two to five years underground, slowly growing until they are ready to emerge. The overlapping generations of annual cicadas create the impression of a steady stream of cicadas every year. In contrast, periodical cicadas spend either 13 or 17 years underground as nymphs before emerging as adults [[1]].
Brood XIX and Brood XIII
The cicadas that are expected to emerge this spring belong to two different broods: Brood XIX and Brood XIII. Brood XIX, also known as the Great Southern Brood, is the largest periodical cicada brood and stretches across the southeastern United States. It appears every 13 years. On the other hand, Brood XIII emerges every 17 years and is found in Northern Illinois [[1]].
The emergence of these two broods at the same time is considered rare. Dr. Jonathan Larson, an extension entomologist and assistant professor at the University of Kentucky, describes it as an "absolute oddity of nature" and one of America's coolest insects [[1]].
Cicada Emergence Timing and Locations
The periodical cicadas will emerge when the soil temperature 8 inches deep reaches 64 degrees Fahrenheit (about 18 degrees Celsius). This is expected to happen sometime in mid-May. The adult cicadas have a life cycle of just a few weeks, but their emergence will be staggered, resulting in about six weeks of cicada activity [[1]].
Different regions in the United States will experience cicada emergence from these broods. Northern Illinois, southern Wisconsin, eastern Iowa, and northwest Indiana are likely to see cicadas from Brood XIII. Central and southern Illinois, most of Missouri, and scattered areas of Kentucky, Tennessee, Virginia, Maryland, North Carolina, South Carolina, Georgia, Alabama, Mississippi, Louisiana, and Arkansas are due to experience cicadas from Brood XIX [[1]].
While there may be some areas where the geographic ranges of the two broods historically overlap, experts suggest that the overlap is unlikely to be significant. The co-occurrence of Brood XIX and Brood XIII at the same place and time is rare and has not happened since 1803. After this year, they will not emerge together again until 2245 [[1]].
Cicada Characteristics and Behavior
Periodical cicadas can be distinguished from annual cicadas based on their appearance. Annual cicadas tend to emerge later in the year, such as in the dog days of summer, while periodical cicadas make their appearance in the spring. Periodical cicadas are smaller and mostly black, with bright red eyes and orange-tinged wings and legs. In contrast, many species of annual cicadas are large and greenish [[1]].
Cicadas are known for their loud singing, which can be heard during their emergence. They use their songs to attract mates. While the noise can be overwhelming, cicadas are harmless and do not pose a risk to garden plants. However, young trees may be vulnerable to damage when cicadas cut into branches to lay their eggs. To protect trees, covering them with cicada nets can be helpful [[1]].
Cicadas do not bite or sting humans or pets. If a dog eats a cicada, it will be fine. In fact, cicadas have been consumed by humans for thousands of years and are described to have a natural, sweet nut flavor. However, individuals who are allergic to shellfish should avoid eating cicadas, as a protein present in shellfish that is tied to allergies is also found in many insects [[1]].
Citizen Science and Appreciating Cicadas
If you live in an area where cicadas are emerging this spring, you can contribute to cicada research by downloading community science apps like the Cicada Safari app. By photographing the cicadas you see and submitting the photos through the app, you can provide valuable information to scientists studying cicadas and their response to climate change [[1]].
Dr. Chris Simon, a professor of ecology and evolutionary biology at the University of Connecticut, hopes that people will appreciate the unique natural phenomenon of cicada emergence. She describes cicadas as some of the coolest insects in America and encourages people to embrace the opportunity to witness their unusual behavior [[1]].
In conclusion, the emergence of periodical cicadas from Brood XIX and Brood XIII this spring is a rare event. These insects follow either a 13- or 17-year life cycle underground before emerging as adults. While the cicadas can be loud and numerous, they are harmless and do not pose a risk to humans or pets. The emergence will occur in different regions of the United States, and citizen science apps can be used to contribute to cicada research.
