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June 28, 2008

What is the purpose of cicadas?

Filed under: FAQs | Magicicada — Dan @ 11:35 am

Here’s a question we get a lot: “what is the purpose of cicadas?” It can be a loaded question, but I think people just want a concrete answer to justify the magnitude of the unusual (why only once every 17 years, why so many) or annoying (inconvenience, noise, ornamental tree damage) aspects of the 17-year cicadas. Every living thing has a reason for existing, a niche to fill, a role to play, a purpose — let’s consider how cicadas fit it to the big picture.

It helps to consider perspective when considering the purpose. I’ll break their purpose down into 4 groups, for this: critters, fungi, trees, and people. Critters first, because their relationship with cicadas is the easiest to explain.

The cicada’s purpose in terms of critters:

Cicadas provide a link in the food chain between trees and critters, which I’ll define as any animal that will eat a cicada. Critters love cicadas, and a 17-year cicada emergence is the single greatest feast of their lives. It’s like 17 years of Christmas, Thanksgiving, and birthday parties rolled into one incredible month.

Trees feed off the sun and nutrients in the soil, cicadas feed off the trees, critters eat cicadas, and alpha predators (wolves, foxes, bears, cats, game fish, people) eat critters. The massive release of food and energy that comes from a cicada emergence results in an explosion of critter populations, which in turn results in a boon for alpha predators as well.

The cicada’s purpose in terms of fungi:

I’m not a fungi expert, but I’m pretty sure different species of fungi have a grand time digesting dead cicada bodies once they’ve died and begin to rot (I’m sure the same is true for bacteria, and microscopic critters). Fungi, of course, become another link in the food chain.

There is one fungus, the Massospora cicadina fungus, that really loves cicadas. The Massospora cicadina spreads via cicada mating and destroys the cicadas entire abdomen in a matter of days. If you’re a Massospora cicadina, from your perspective, the cicadas purpose is to provide you with nourishment and a home. Gruesome, but true.

The cicada’s purpose in terms of trees:

Periodical cicadas are parasites of trees, more specifically of deciduous trees (leaves fall off in the fall) native to the region in which the periodical cicadas exist (maples, oaks, ash, etc.). The term parasite has negative connotations, but in the grand scheme of things, parasites can benefit their hosts, or other species by keeping their hosts in check.

Cicadas provide trees a service by pruning the weak branches of a tree. Cicadas lay eggs in the branch, weak branches wither and die (“flagging”), and the tree benefits from that by not having to waste energy on a weak or diseased branch.

Cicadas also do the trees a service by dying and releasing a vast amount of nutrients back into the soil. When the cicadas die, it’s like dumping bags of fertilizer around the roots of the trees. The extra nutrients should result in a spurt in tree growth and seed production the following spring, which would result in an increase in tree populations (and acorns, which critters love to eat).

A small percentage of small, weak trees will die during each emergence, particularly non-native species (like imported ornamentals). This can be frustrating for people concerned with the landscaping on their property, but in terms of trees in general, it’s not as bad as it seems. The fertilizing and pruning cicadas perform will actually benefit the older trees in such a way that will encourage them to produce more seeds the following year. Any loss of trees will be balanced by gains in the following years. Also, cicadas may do native trees a favor by weakening or killing non-native ornamental trees, which compete for the native tree’s food.

The cicada’s purpose in terms of people:

Cicadas are a food source. Many people around the world eat cicadas, and not just “on a dare”, but as a delicacy or staple food. Cicadas have made more than one appearance on Bizarre Foods with Andrew Zimmern for instance. Native American peoples also ate cicadas too — and in at least one case it kept a tribe alive during hard times. In most places, though, cicadas are not a sustainable found source, so insectivore gourmets should rely on easily farmable insects like crickets, waxworms, and mealworms.

Cicadas provide people with a job. Those people include professors and researchers like Gene Kritsky or John Cooley, scientists, and landscapers.

Cicadas provide people, including me, with a hobby. There are a lot worse things you can do with your time.

Cicadas provide artists and musicians with inspiration. There are bands and albums named after cicadas, and many songs inspired by cicadas.

Cicadas defending America? Could be. The Navy is researching cicadas according to the Massachusetts Cicadas site.

Cicadas provide memories. If you think about it, we people don’t have all that many milestone experiences in our lives: we have our first day at school, graduations, we get our first car, weddings, we buy your first house, children are born, loved ones pass away, special vacations, and maybe we experience a flood, fire or other unfortunate but remarkable events. A periodical cicada emergence is remarkable because it not only places a memorable milestone in the timeline of our lives, it places a series of them; a series of milestones, 17 years apart, and not only within our lives, but linking our historical timelines to the timelines of your children, and grandchildren. Gene Kritsky calls cicadas the insects of history, and I think you can understand why.

Recently, cicadas were discovered to have microscopic structures on their wings that destroy bacteria. This is discovery is being used to inspire medical advancements, such as antibacterial cornea replacements. Amazing.

Some papers on this topic, and other scientific uses for cicada wings and skins:

Cicadas can also be used to gauge soil pollution, as they spend most of their life in the soil they absorb the chemicals introduced into the soil from human pollution.


  1. Judi Henderson says:

    Two questions.
    1) Is there a time of day when they are less likely to be flying around? I am truly terrified of these insects, even though I logically know they are harmless and do good for the trees, it does not calm my terror.
    2) I am fortunate to have a large amount of humming birds which I provide sugar water here in Gordonsville, TN. Will this years (2021) cicada emergence keep them away? The hummingbirds are not much bigger than the cicadas, and they may fill the trees so much that the hummers will not find a nesting site.

    1. Dan says:

      @Judi — usually before 10am and after 5pm they’re less active. Also cloudy, cool and definitely rainy weather calms them down.

      Cicadas disturb birds in general. I’ve heard that they scare hummingbirds away, but they do come back once the cicadas die off — last week of June.

  2. Matt says:

    Seems like cicadas would be very helpful at keeping life on earth in an extinction event.

    1. Dan says:

      I think they survived the meteor that killed the dinosaurs.

    2. lee says:

      like this theory

  3. Katharine Layton says:

    I believe cicadas aerate the soil. After an emergence my place looks like I had spent a fortune to have it professionally aerated. Also my dog binge and purges them. Yuk….but he’s so happy!

  4. nina says:

    Noticed that a cooler temperature over night and next day, seemed to slow down the emerge process of cicadas for one day. Not sure if just a coincidence or not. Also, how many days after cicadas have emerged, and flying around do they live? I’ve heard they only live a few days, is this true?

    1. Dan says:

      Cool weather curbs their activity. They can live upto 4 weeks in their adult stage, but usually they’re killed before that.

      1. Lynn Pennington says:

        I live in South Carolina, I just witnessed one this morning emerging from its shell, I’m gonna say pretty fascinating !! He’s attached to my habbernero pepper plant pot .. how long will he live there?

        1. Dan says:

          Probably another few hours. Then it will crawl or fly away once its skin is hard enough.

  5. Kenn and Cheryl Sickle says:

    Thanks for educating us about cicadas. Right now we’re overrun by them (Brood 5) in the Ohio River Valley.

  6. Bev Carroll says:

    Why do cicadas attach to some houses and not others ? I noticed they are also attached to the tulip stems. Why?

  7. PJ Hayden says:

    Thanks for the explanations of the cicadas purpose. I figured they were good for something. It seems they are good for a lot of things. I DO wonder what state they exist live in, for 17 years?

    1. Dan says:

      For the 17 years they’re underground, building tunnels and living structures (called cells) and feeding from the roots of trees.

    2. Kathy S says:

      Midwestern states are their natural habitat. Definitely in Ohio!, West Virginia, Kentucky

  8. Susan Gayhart says:

    Why are they called 17&13 yr cicadas when I see and hear them every year?…also this year 2015 I started to hear them on June 4th. Are we in Missouri going to have a very early frost? Because I don’t usually start hearing them until August.

    1. Dan says:

      There are over 190 species of cicadas in the USA. Only 3 of which are 17 year cicadas, and 4 are 13 year cicadas. Along with the 185 species of cicadas that can be heard every year, there are hundreds of other insects that might sound like a cicada, along with frogs, birds and machinery that might sound similar. So that is why. Of course, a full-blow 17 year cicada chorus blows everything else away, and you would never confuse it with any other cicada or creature.

    2. Dan says:

      Also, these are not the species associated with a early frost — those are called Tibicen. There are plenty of sound files and pictures of those on the site. Start here.

  9. ben says:

    why do cicadas like to land on people soo often

    1. Dan says:

      There are so many of them, it really doesn’t matter if a few of them (or a lot of them) get hurt/eaten. After a week or so, they get a little more timid.

  10. ben says:

    why do cicadas make soo !!! NOISE

    1. Dan says:

      They’re trying to meet other cicadas. Find a wife, have kids.

  11. Marisa says:

    Yeah I forgot to proof read. Who is treating the earth badly and who is caring for this precious planet. Swipe!

  12. Marisa says:

    Cicadas come out to check on the earth. They keep tabs on
    who is tearing it badly a’s who is caring sure this previous planet. Hope you’re not like my neighbors who love cutting down trees! They’re natures guardians. Good luck! I know they love nt yard and they are most welcome.

  13. karol says:

    Aside from the fact that they are constaantly flying into my head, I don’t have a problem with them. I didn’t know they te the trees. I get the weak parts, but I just planted some fruit trees this year, will they hurt those?

    1. Dan says:

      The could. Just knock them off or net the trees.

  14. Syd Fuller says:

    Thanks so much for this. Cicadas seemed extremely pointless to me before I read this. I still hate them, but thanks.

    1. Lilly C. says:

      My feelings exactly.

  15. Matt says:

    Thanks for posting this… as we prepare for “Brood II” I’ve been doing some research, mostly to find out if there would be an issue if my dogs happened to munch a few while out doing their business. For the record, they can be “food” for dogs just like humans, but over consumption, much like any other food, can cause GI issues and too much chitin (shells) can stuff them up. Glad to have some other good info to go with it.

  16. Dan Gidez says:

    One of my fondest memories comes from when I was 14, my cat escaped during the cicada swarm, when I got him back inside he was purring and being very playful. I picked him up and could hear he swallowed a cicada whole, it was buzzing in his stomach, I didn’t see how this could be possible as the cat has teeth/stomach acid nevertheless the cicada was in there buzzing away, too funny. It took less than 5 minutes for the cicada to die but while it was alive the cat seemed to love it. Many old timers tell their age by cicadas, especially white trash mountain folk like myself. The first time you see a cicada swarm you are a young child, the next time you see one you’re in highschool, the next time you have a job and a family, the next time the kids are off to college and the next time you’re ready for a nursing home, any more sightings after that are a blessing because you will probably be too old to hear them again,at most one more time and thats the end. This of course excludes dog-day, 7 year, and 13 year cicadas..

  17. Craig says:

    My co-worker is deathly afraid of the cicadas; to the point of tears. Does anyone have any ideas to help make her more comfortable during this year’s visit? I’m afraid that she may be trapped in her home for two months while the cicadas take over her neighborhood.

    1. Dan says:

      Well, first, they might not show up in your coworker’s yard. They don’t show up everywhere. Only randomly and where trees have not need removed from the yard.

      Second, they won’t be around for two months. One month max.

      Third, they don’t spread disease, they are not venomous, and I’ve never heard of a case of a cicada harming a person, even accidentally.

      Fourth, they really are quite docile.

  18. Barry d. says:

    I notice an increase of cicadas on my garage and home. I wondered why and thought maybe it was because I cut a maple tree down just before the cicadas came out of the ground this summer. Perhaps there was several 17 yrs ago on that maple tree? when they come out of the ground do they tend to migrate toward the tree they started in?

    1. Dan says:

      My folks had a cicada emergence where an old apple tree was cut down, three years after it was cut down. The roots of the tree probably remained alive.

  19. sue says:

    I’ve noticed our backyard birds have largely disappeared since the 13 year cicadas are in our woods. Squirrels are scarse also. Are they eating cicadas? Thanks, Sue

  20. Ellen says:

    I actually want to thank you for all the information on cicadas. I honestly hated them, but then when I read this I realized that they have many purposes and really are sad little creatures that help more than they hurt. I feel sorry for them a bit, because their main purpose is just to provide: help feed the birds and make trees & seeds grow better the next year. I think they are misunderstood. With this huge outbreak, the next time someone says, “I HATE these things!” I will try and change their minds, because really they aren’t that bad. I used to play with them when I was little, and now I realize my mom let me because they were harmless to me. That’s why I feel bad for them I think, because they are truly helpless! (No stingers and they don’t bite!)

  21. Jacqui Wade says:


    Thanks for the good answers to my question. The answer about the crows makes great sense to me. Today, I saw a squirrel munching on a dead cicada! Hey, they are edible and some human cultures love to eat them. So, why not squirrels? Have a great weekend.


  22. Jacqui Wade says:

    My property is infested with “13 year” Cicadas, and that is O.k. now that I’m use to them and know that soon their season will be over. However, I noticed that for the first few weeks of their presence, I did not see the usual birds–mainly Crows–that also inhabit my area. Don’t birds eat cicads? What are the cicadas’ natural predators? I live in middle Tennessee. I would very much like an answer to my questions. Thjanks.


    1. Dan says:

      Cicadas true natural predators are a species of fungus, and underground, moles and voles. Above ground pretty much anything will eat them, but a few things can happen that can happen that make birds shy away:
      1) cicadas use a strategy called predator satiation; they purposely sacrifice their lives as food for predators, so the predators get full of cicadas, and some are able to escape and mate. Imagine the birds feel like they’ve eaten a big Thanksgiving dinner — they just go off to snooze in front of the tv and digest the food for a while (the bird equivalent of tv).
      2) the calls of cicadas might annoy crows so much that they avoid them. I believe birds like crows rely on a more complex set of calls to communicate than most birds, so being able to hear each other could be very important to them, so they intentionally avoid the sonic interference caused by the cicadas.
      3) predators are not accustomed to these cicadas because they only emerge every 13 years. some predators probably are eager to avoid the “insanity” of a cicada emergence. I know a lot of people would not blame them.

      1. Brian says:

        What about the Cicada stinging hornets? They seem to show up at the same time as the Cicadas.

  23. D says:

    I was wondering why God put Cicadas on earth, so many people seem to be complaining about them! I think they’re great. The last time they came around I was a little girl and I remember whacking our bushes with a stick and literally an entire beach bucket full of them would drop in, it seemed like so much fun for my brother and I! But now, I just feel a lot of respect for this bug, I mean a 17 year old bug? Whose ever heard of another one like that?? It’s amazing, I can’t believe I have to wait another 17 years to see them! They are very interesting, so much so I got online to do some research because I really don’t know too much about them. Between the encyclopedia with info. on Brood 14 and your opinions on their purposes, I feel a little more enlightened. Everyone give Cicadas the respect they deserve. They’re only here for a short time, like a comet, enjoy it!

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