Cicadas emerge in Tennessee after 17-year hibernation

By KATE COIL
TML Communications Specialist

Cicadas are already emerging across Tennessee, but rather than as a pest or nuisance, UT professor Dr. Jerome Grant said cities can use their arrival as a chance to educate residents about an important biological phenomenon.


Grant, professor of biological control and integrated pest management with the University of Tennessee Institute of Agriculture, said there are many misconceptions about cicadas.


“A lot of people think of this as an invasion of an insect, but it’s not an invasion,” he said. “These insects have been underground for 17 years, and all they are doing is coming out to live their lives. This is a natural phenomenon that only occurs every 17 years. The last time this happened George W. Bush was president and we won’t see it again until 2038. I would encourage municipalities and families to use this as a learning experience, to talk about these insects and the odd life cycle they have.”


Grant said cicadas are defined by “broods,” which refers to the different years in which they emerge. The brood that will be emerging this year is known as Brood X and is one of the 17-year cicada varieties. Those who were living in Tennessee in 2004 will remember this brood as that is the last time they were seen in the state. There is a difference between these cicadas and those that appear every year.


“The annual cicadas are generally referred to as the dog day cicadas because of the time they come out,” Grant said. “They typically come out during the summer, and we do have them every year. The difference is there aren’t many of them. The ones that are coming out now are known as periodical cicadas, and they come out every 13 or 17 years. They live underground for 99% of their life and are only out for a couple of months. Their sole purpose for coming above ground is to reproduce. The new progeny then drop down to the ground, and we don’t see them again for 17 years. The dog day cicadas are also a larger cicada and are more green in color. The periodical cicadas have an orangish-red coloration and are smaller than the dog day cicadas. The major difference in the two is the numbers.”


Brood X is one of the largest broods of cicadas, and there can be about a million cicadas per acre in the areas with the highest intensity of the brood. There are approximately 15 different periodical cicada broods that live in the U.S. Grant said Tennessee will join about 15 other states across the East Coast and Midwest who will see cicadas this year.

“Not every area will have large numbers,” Grant said. “If the number of cicadas was heavy in your area in 2004, it will be heavy again this year. If it was light then, it will probably be light this year. And if you didn’t have cicadas then, you probably won’t have them this year. This particular brood is heavier in East Tennessee than it is in Middle and West Tennessee, though there will be pockets throughout the state that will see them.”


However, just because an area doesn’t see cicadas this year doesn’t mean it will be cicada free in the future. Grant said there are two broods expected to emerge with heavy concentrations in Middle and West Tennessee in 2024 and in 2025.


“While Brood X covers the widest geographical area, we also have a 13-year cicada known as Brood IXX that comes out in 2024,” he said. “They will come out mainly in Middle Tennessee. Then there is Brood XIV that is another 17-year cicada who will come out in 2025.”


Typically emerging around Mother’s Day, Grant said temperature plays a big role in when the cicadas come and when they go.


“These cicadas will not come out of the ground until the ground temperature is 64 to 67 degrees at four inches deep,” he said. “We have had a cold spell the past week or so that has knocked the populations back from emerging. Because of the cold, they haven’t emerged every year. The adults live about six weeks, so you can expect them to be gone by the end of June. You get few numbers in early May and few in late June, but you may have a four-week period with high numbers in between.”


While Grant said cicadas can sometimes seem “like something out of a horror movie,” they are pretty much harmless for people and pets.


“Cicadas do not bite and they do not sting,” he said. “They pose very little danger to humans and animals. The only issue I have seen with animals is that you see dogs sometimes biting at them because there are so many of them. Eating cicadas may cause pets to get sick. That is the only potential threat they have. They can be scary because they can get on you, but they won’t hurt you. The only real harm they cause is the sound they produce.”


These annual cicadas are most known for their high-pitched, shrill sounding songs that are part of the mating process.


“The males are the only ones who make the sound, and they make the sound to attract the female to reproduce,” Grant said. “The male tries to make the loudest sound so he can out compete the other males for the female’s attention. All the sounds you are hearing are solely for the purpose of this insect continuing its life cycle. The noise can be between 80 to 100 decibels, which is like a loud lawnmower.”


While the male cicadas make noise, the female cicadas are the ones responsible for damage to vegetation. Grant said that many people actually do not understand what it is cicadas do to plant life.


“They don’t do feeding damage on trees,” Grant said. “The female has a knife-like egg-laying device known as an ovipositor. She will go down the twig, cut a slit with that, and then lay an egg in the slit. Because of those slits, that twig dies. It will turn brown and break off, which can cause deformities in the tree.”


Fruit trees like apples and pears as well as dogwoods, oak, and hickories are popular targets for cicada egg-laying. For those who want to protect their vegetation from this, Grant said there are some steps to take.


“First off, don’t use pesticides,” he said. “If you use pesticides, the females are still going to do the egg-laying that can damage plants. It may kill some of the cicadas you see on the tree, but there will be many more who come back on that tree. We encourage people, particularly municipalities, to hold off on planting until July or sometime after. The dog day cicadas do the exact same thing, but they don’t have the numbers to do the damage to plants the periodical cicadas can. If you do have a new tree that you want to protect, some people cover them in mesh so they can still breathe. Of course, if you don’t have high density cicadas, it may not be worth it to do anything.”


In the long-run, Grant said cicadas actually provide more benefit for plant life than they do damage during the brief period they emerge.


“For 17 years, they feed underground on the roots of trees,” Grant said. “Cicadas are beneficial to us, and I think that is something that people need to remember. Cicadas are excellent soil aerators when they are underground. When they come above ground, they are food for a lot of animals. When they die, their bodies provide a lot of nitrogen, minerals, and nutrients back into the soil. They are also natural tree pruners.”


Those who are particularly adventurous can even consider eating cicadas themselves.


“If you’ve never done it before but have considered trying edible insects, cicadas can be eaten by humans,” Grant said. “It is an interesting way to add another dish to your menu.”

Overall, Grant said cicadas provide a unique opportunity to learn about Tennessee’s natural resources.


“This only occurs four or five times in a person’s lifetime,” he said. “Instead of looking at it as a negative thing, I would encourage municipalities to discuss it and talk about it, to learn a little biology and about nature. It is important that we learn more about our world.”
Grant encourages municipal officials to contact their local UT Extension Office for educational resources and presentations on cicadas.


For additional information on cicadas, also visit https://news.utk.edu/2021/05/06/cicadas-fact-or-fiction/ or at https://www.tml1.org/sites/default/files/tml/images/periodical_cicada_extension_publication_ut.pdf