Saturday, September 12, 2009

Cicada shells


Almost every summer I receive several questions about strange bugs sitting motionless on fence posts, tree trunks, and other upright objects. I thought I would do an entry here to explain the mystery.

The descriptions of the creature that people give to me vary from a “cross between a crayfish and a beetle,” to “gnome-like,” and all mention the large claws on the “front end.” No one has ever seen anything like it, and it is no wonder. Normally, the creature they are seeing lives fairly deep underground.

I have taken to calling these bugs “former insects,” since the objects being seen are not entire insects but the cast exoskeletons (“skins”) of cicadas, family Cicadidae. Scientists call these shed skins “exuviae,” all that remains behind when the insect molts from the nymph stage into an adult. Dragonflies, damselflies, stoneflies, and mayflies also leave behind these ghostly but tangible shadows of their former selves.

The average person rarely sees an animated version of a cicada nymph because the mature nymphs emerge from the soil at night, climbing the nearest vertical surface, and then splitting the exoskeleton down the middle of the back to allow the escape of the wet, soft adult under the cover of darkness. The fresh, pale adults are extremely vulnerable, but their principle predators are diurnal, so they avoid instant death by coming out at night. Cicadas are large insects, so they can be quite conspicuous under the best of cryptic circumstances.

An adult "annual" cicada, Neotibicen sp.

Most people in eastern North America see the shells of “annual” or “dog day” cicadas in the genus Tibicen. They then hear the loud “songs” of the adult male cicadas, not often seeing the insect that makes such a racket. Despite the name, annual cicadas still take a long time to grow up. They live a subterranean existence as nymphs, sucking the sap from tree roots for at least five to seven years. The generations are staggered, though, so some adults emerge every summer. This is in contrast to the synchronous broods (populations) of the periodical cicads or “17-year locusts” that emerge en masse in the late spring or early summer every 13 or 17 years, depending on the latitude of the population.

I like to get questions about things like cicada exuviae. It shows that people are observant and curious, two qualities I really admire in my own species

67 comments:

  1. I remember as a youth in South Africa, walking through a forested area near the town of East London, the cicada 'hulls' crackling underfoot.

    Just a bit eerie...

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    1. When my grandfather was still alive we used to make a game out of finding the cicada exoskeletons (we would call them shells though) n stepping on them lol whoever stepped on the most "shells" won... good times lol

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    2. Crunch, crunch, crunch, crunch! :-)

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  2. It is funny we don't see more of these shells, considering their size and the relative abundance of cicadas in the summer. Last year I saw one for the first time - and also got the opportunity to watch an adult emerge. Strangely, it was at midday... http://themarvelousinnature.wordpress.com/2008/08/09/arrival-of-the-dog-days/

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    1. I live in West Omaha and I see their shells attached to walls. Maybe it's the neighborhood you live in. But when there is more trees there are more cicadas shells

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  3. This sounds so odd. I'm surprised cicada exuviae still surprise people. Mind you, I grew up in the south where summer wasn't summer without all the discarded exoskeletons and the days full of cicada song. Maybe my POV is a tad skewed. But as you say, it's at least good that people are seeing new things and wanting to know what they are.

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  4. Hi, can you help identify a bug I posted a photo of it on my blog. I live in Wyoming near Yellowstone and this large grasshopper like bug (doesn't jump fast or high though) started appearing last month. I see them on the trails a lot. Please see the photo on my blog today and help me i.d. it. Thanks.

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  5. I identified Human Footprint's mystery insect as a female "Mormon cricket," Anabrus simplex; I think that there may literally be fewer cicadas than in years past, at least in urban areas where sprawl has literally paved them over. Further, before the internet, people mostly just wondered about such things because they did not have ready access to "experts." The WWW now provides those opportunities. I find my questions from men are often 'nostalgic,' inquiring about insects and arachnids seen decades earlier.

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    1. Returning to my home state of IA after years in CO & WA - I've been learning so much about things I took for-granted as a kid! Thanks for the informative article!

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  6. Thanks Eric for visiting and identifying. Seems like they might even be good eating as I read that Native Americans as well as coyotes ate/eat them. I think I'll be satisfied with just knowing their i.d.

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  7. Great article! I just posted a photo of a cicada shell on Instagram.

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  8. What are the white stringy pieces left in the Shell after the cicada hatches ?

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    1. I believe those are the tracheal tubes (breathing system), but I cannot be positive. I am not an insect physiologist. Excellent question, though!

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  9. its weird, i have at leaset two of these on each of my oak tree trunks. If this is rare i am curently looking at 8 of them. What does this mean??

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    1. No, cicadas are not rare at all. Very abundant, in fact! I simply find that people who have not seen them before are perplexed by them (the shed exoskeletons especially).

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  10. I haved lived here for 15 years and have never seen this before. I have a mason jar full...my family thinks im crazy...lol@!

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  11. A nymph is in my house! It was on it's back wiggling around so i scooped it up into a jar and am hoping to watch it molt! It is freaky looking, my 5 year old daughter called it dinobug!

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  12. i actually had a cicada crawl into my bed! it was so cool

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  13. My bradford pear is 20 this year. First time noticed yellow leaves all around base of tree. Lots of them. Investigate and saw the shells around the trunk. Can they harm the tree. Doubt it but wonder...dottie

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    1. You'd think they certainly would do damage to the tree by feeding on the roots....but they rarely if ever do. Females *can* damage trees in the act of ovipositing (laying eggs). They can break or girdle a twig causing "flagging."

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  14. So is there anything in it or is it just the left over of the shell

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    1. It is the old exoskeleton. The insect molted.

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  15. I saw a cicada moving around on my Iris and the next day the shell had formed. This was yesterday and so far he is still in the shell. How long before he emerges?

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    1. I wish I could answer that. It could be that it was parasitized, in which case some other insect might emerge instead of a cicada.

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  16. I currently moved into a new house. We have been here maybe 30 days. Every few days I find multiple exuviae. I have 23 in total. I have video of one climbing out.Also two that did not make it out at all. I have amired them since I was a youngin. People think I am crazy but I have a jar full.

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  17. Wow! I thought it so strange that these bugs were in the exact same place on the tree trunk every day. I could not rest until i found out. Thanks for the explanation! :)

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  18. What do you call the orange colored mushroom like that grown in the cicada shell when it's still underground?

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    1. I have no idea what you have reference to.

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    2. I was looking about it in the net and found that it is a fungus. Is it part of their life cycle?

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    3. Cicadas, like most insects, are attacked by fungal pathogens. It is NOT part of the creature's normal life cycle. The fungus ENDS the insect's life.

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  19. how long does it take for the cicada to emerge from it's shell and be fully formed (but still moist)?

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  20. I have seen an unusual amount this year. I have an oak tree in my front yard and there are literally hundreds. why so many this year.

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  21. Where do they go when they leave the shell, die or what

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    1. They go about their adult lives of finding mates and reproducing.

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  22. I have a video that my dog and i hung out a while at a pine tree to record . Pretty awesome. Shows it coming out of its shell . Ive always just seen the hulls but we caught this one in progress.

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    1. During the day or at night? I Would do anything to see one coming out!

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    2. Cicadas usually emerge from the ground and molt into adults during the night, but sometimes you can find them in the morning.

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  23. I started collecting the shells when my children were small they love it. Every Sunday after church we make our rounds. My son has hundreds. It is very cool.

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  24. I took my three children to the park about 5 min ago. We have found over 20 of these cicada shells. The kids have ran from pine tree to pine tree collecting them! They have enjoyed it very much!

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  25. I love these creatures I have an exoskeleton.

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  26. Found about 6 on my pine tree here in MI. Thanks for great explanation!

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  27. No one has mentioned that their sharp claws let them hang very nicely on clothing. Growing up in New Jersey, when we found one of these we automatically hung it on our shirt as a startling decoration.

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  28. I've seen them ever since I can remember, but we have always called them locusts. Is this just being a hillbilly 😆 lol I had to look up insect that she'd a brown shell to find out what it was called. Does anyone else call them locusts, or just back woods Texas.

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    1. That is exactly how I found this! I always called them locust too lol. Back yard Louisiana. No but seriously I was asking my husband and he thought the same thing so I looked it up. I have read so many interesting things on this website I love it.

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  29. No you're not the only one that thought they were locusts. Found out today differently my neighbor told me its real name. I feel deceived my whole life lol.. I live in Phoenix AZ and growing up here we use to have a Weeping Willow tree in our front yard. We collected their shells too , it was fun. Looking back now it's very creepy looking lol. Thank you Bug Eric for explaining this to us, very informative and interesting . 😊

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    1. You are welcome; and thank you for the kind sentiment.

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  30. I am from Wisconsin,but currently reside in Lawton/Fort Sill, Oklahoma. Today while outside with my grandson and he said granny what kind of bug is that, surprisingly, I remembered from my of being a resident camp counselor at near Michigan

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  31. I've picked a few shells off my shed and fence this week(July in NJ ) I also saw one burying itself in my yard. Thanks to this link I now know what they are 😊

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  32. I went outside once at night and went back in and layed on my bed and i felt and heard a buzzing sound. The crazy thing was on my back and every time i moved he buzzed.lol i turned him loose outside

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  33. Thank you for solving my investigation of what I have found in my garden in No.Jersey. I have only 2 in a jar but I figured I would save them for the 5th grade science teacher in the school I work at.

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  34. What do they look like when they come out of the shell?

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    1. Fair question! I have updated the post to include a picture of an adult cicada.

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  35. I am in knoxville tennessee and I live with my grandma and she has a pine tree in her yard she has like a hundred on the tree they are weird looking and they are fun to watch

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  36. I have thousands of shells on and around my trees. What happens to the shells eventually?

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    1. They eventually weather away and decompose. It may takes years, though.

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  37. Although, I am creeped out by them.. thank you for the information .A few questions are they harmful.. do they bite.. and do they live through the winter or do they a have a short life span? I have a dead adult cicada on my porch now and it is huggggee😬🤦🏾‍♀️

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    1. Cicadas are seldom harmful. They feed on plant sap with straw-like mouthparts, so no, I have never heard of anyone being bitten by one. Yes, they live through winter, but as nymphs underground, not as adults.

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  38. Just saw one as it was breaking free from it exoskeleton. So glad i was able to face time my nieces and nephew and experience it all together. So glad I found this article to know more about what I finally got to see in person. Im 52 and felt like a kid as I watched it wiggle itself out! Thank you for the great article!

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  39. I have always seen these shells on the pine trees in Georgia. Tonight I could hear them calling at each other in the wetland of my property. They are very loud! They seem to be from out of space!!!

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