14 Facts About Periodic Cicadas

14 Important Things to Know

Periodic cicadas emerge in swarms
Periodic cicadas emerge in swarms. Photo by Greg Hume

What do you know about periodic cicadas? Following are 14 common questions and facts that you need to know:

1. I saw a bug the other day that I thought was a grasshopper, but my friend said it was a cicada. What is a cicada?

A cicada can generally resemble a grasshopper and is similar in that it does not cause harm to people or pets, but can damage plants. However, the life cycle and habits of the cicada are very different than that of the grasshopper.

While there some cicadas that appear every summer, there are a number of North American periodical cicadas that live most of their lives underground, emerging only once in 13 years or 17 years, depending on its brood.

2. What is a brood?

The definition of brood by Merriam-Webster.com that is applicable to cicadas is "the young of an animal or a family of young; especially the young (as of a bird or insect) hatched or cared for at one time." Thus, each brood of cicadas is a grouping of the species that all emerge at once.

3. How many cicadas emerge at once?

A lot! According to John R Cooley, who hosts the website magicicada.org, it is most common for hundreds of thousands of cicadas to emerge per acre, but population densities have been known to be as high as 1 1/2 million cicadas per acre – all emerging at once.

4. Are these 13- and 17-year broods only in North America?

Yes. North America also has cicadas that reappear annually, but it is the only biogeographic region where the periodical cicada, Magicicada genus, exists – which lives for up to 17 years, but spends more than 99 percent of its life underground.

In general, the 17-year cicadas are found primarily in the Northern states and into Canada, while the 13-year cicadas live primarily in the Southern and Midwestern States.

5. What do the cicadas do when they swarm out?

The cicadas swarm out from the ground as nymphs or larvae. But because their primary purpose is to mate to create the next generation, they will climb up into a tree to shed their nymphal "skin" and make their final transition to adult.

This is critical because once the periodical cicada emerges from the soil, it will live for only about 6 weeks. The males will "sing" to attract the females, then once they mate, the female will lay up to 25 eggs at a time into the branch of a tree.  A female cicada may lay more than 500 eggs in her short lifetime.

6. When do the cicadas go underground?

Although the adult cicadas will die in a month or two after emerging (or be eaten by predators), the eggs that were deposited into the tree will hatch and feed on the fluid of the tree. The nymph will eventually drop down to the ground and burrow 6 to 18 inches down into the soil where it will begin feeding on roots. It will live and feed beneath the ground until it is time to emerge.

7. What causes cicadas to emerge?

In the spring of the 13th or 17th year, the cicadas will begin tunneling upward, creating exit holes of about 1/2-inch in diameter. Once the ground temperature around the exit holes reaches approximately 64F and the sun sets the cicadas will begin their emergence – with all those of a brood emerging at about the same time of year for every 13- or 17-year cycle. There may, however, be some variation based on weather temperature.

Because their emergence is based on temperature, it is no surprise that southern cicadas will generally emerge sooner than northern cicadas. However, whether north or south, all the cicadas of a region will emerge at the same time.

8. Why do cicadas only come about every 13 years or 17 years?

It's not really known for sure why the Magicicada appears so infrequently, but there are a number of theories:

  • Like most insects, cicadas have natural predators, including the praying mantis and cicada killer wasp. So some scientists theorize that the cicadas may have evolved to the long underground life cycles in order to evade and throw off their predators.
  • The massive emergence of high populations of cicadas may also have been an evolutionary adaptation to thwart predators. With so many emerging at once, it would be nearly impossible for the predators to attack them all, thus helping to ensure the survival of the cicada species.
  • Another theory is based on the actual numbers of 13 and 17 as the emergence years. Both are prime numbers – meaning they are not divisible by any other number except 1. This makes it very difficult for a shorter-living predator or parasite to attempt to match its lifecycle with that of the cicada, again helping to enable the cicada species to survive, and possibly causing a parasite species to become extinct.

If most cicadas only come out once in 13 or 17 years, why do we seem to hear there is a problem with them somewhere every year?

9. Where will the next broods of cicada broods emerge?

Broods are described by number, using the Roman Numeral system. The most recent and upcoming broods of periodical cicadas and general areas of emergence were and will be:

  • 2015. 17- year Brood IV emerged in Iowa, Kansas, Missouri, Nebraska, Oklahoma, Texas.
  • 2015. 13-year Brood XXIII emerged in Arizona, Illinois, Indiana, Kentucky, Lousiana, Missouri, Mississippi, Tennessee
  • 2016. 17-year Brood V is expected to emerge in Ohio, Pennsylvania, Virginia, West Virginia
  • 2017. 17-year Brood VI is projected to emerge in Georgia, North Carolina, and South Carolina.

A complete table of both 13-year and 17-year broods and their recent and expected emergence years are available at the University of Michigan Museum of Zoology Periodical Cicada page.  

10. Do cicadas bite or can they hurt my family or my pets?

No. Cicadas cannot bite – or sting. If held for too long, however, a cicada may attempt to "feed" causing what feels like a tiny pin prick.

11. What damage do cicadas do?

Because the cicadas feed on trees and their roots, they can cause damage to this foliage. The below-ground feeding of the nymph can stunt the growth of trees on whose roots they feed. Once emerged, the cicadas will move to the nearest trees to feed. When the emerging population is high, the cicadas can cause extensive damage, however, for most mature trees, the damage is generally not long-lasting.

12. How can cicadas be controlled?

Although cicadas generally do not cause long-lasting damage to mature trees, young or small trees or shrubs, and fruit-bearing trees, can be subject to significant damage.

Additionally, their high numbers can be a significant nuisance, thus control can be needed. Following are some natural, non-chemical, and chemical options for cicada control:

  • Natural – Although their high numbers make it impossible for natural predators to eliminate the cicadas altogether, certain species of birds, wasps, and fish will feed on the adults, somewhat reducing the numbers. And, by joining the evolving trend toward entomophagy (insect-eating by humans), you can help to naturally control insects through your own consumption! Even Bon Appetite has posted cicada recipes. Or, if you prefer not to eat them yourself, you can try fishing with cicadas.
  • Non-chemical – If you are in an area where cicada are expected to emerge, you can take preventive steps to protect young or small trees from female egg-laying by loosely wrapping the branches with a mesh cloth. Covering the trunks of small trees or young vines can keep nymphs from climbing up at all.
  • Chemical – Although pesticide application is not generally advised for cicadas because their numbers make it impractical, there are some insecticides registered for trees that can be applied before the female lays her eggs. You can judge this by listening for the male to begin his song. Once he starts singing, wait a week to 10 days, then make the application. The application may need to be repeated more than once. For pesticide recommendations, consult your local garden center or a pest management professional. Always thoroughly read and follow all label directions when using any pesticide product.

13. Now that you mention their songs … I think I've been hearing cicadas. What do they sound like?

It depends on where you live and what species has emerged. The website, insectsingers.com, provides recordings of a variety of different insect "songs" – particularly those of cicadas of the United States and Canada. The sounds are even distinguished those found in the Eastern U.S/Canada and in Western U.S., then further differentiated by species – with a new addition of cicada songs from around the world. The variety of songs among the species is surprisingly, and amazingly, different. Check it out for yourself at http://www.insectsingers.com.

14. I'm interested in the cicada research. Is there anything I can do?

Yes. The reason we know as much as we do about cicadas is because scientists are continually conducting research. If you are just as interested as they are, Cooley also lists a number of projects to which you can contribute:

  • The Simon Lab Nymph Tracking Project is seeking volunteers to help them find periodical cicada nymphs underground. Because nymphs grow at different rates, comparing growth rates of nymphs from different places can help scientists understand their life cycles and the differences between 13- and 17-year cicadas. To determine this, DNA and RNA will be extracted from specimens to identify genes related to life cycle control. For more information and instructions on How to dig for periodical cicadas, visit Simon Lab Nymph Tracking Project.
  • The Magicicada Brood Mapping Project. To determine exactly where broods emerge, scientists conduct a mapping project for particular broods. With Brood V expected to emerge this spring in Ohio, Pennsylvania, Virginia and West Virginia, the project will begin about in April 2016. Watch this site for updates.