Cicadas Explained

After a 17-year stint underground, the first of the Brood X cicadas have emerged from Washington area soil to eat, mate and bring forth the next generation. With 100,000 to 1.5 million cicadas per acre, most area residents will be meeting these visitors face-to-face. But what are cicadas? Why do they only emerge every 17 years? Why do they make so much noise?

Ed Lewis, assistant professor in the Virginia Tech Department of Entomology, was online Thursday, May 13 at Noon ET, to field questions and comments about the arrival of the 17-year cicadas, their life cycle and what they'll do while visiting the metro area.

Dr. Lewis is responsible for developing Integrated Pest Management (IPM) programs for the horticulture, landscape and turf industries in Virginia, with emphasis on incorporating new pest management technologies into current production and management systems. He has a primary appointment in research, which is focused on the ecology and management of turf and landscape arthropod pests. Specific research interests include soil ecology, host-parasite relationships, predator-prey interactions, interactions between insect pathogens and target and non-target organisms, behavior and ecology of entomopathogenic nematodes, and biological control of plant-parasitic nematodes. The cooperative extension program focuses on development and delivery of educational programs necessary to make appropriate decisions for pest management. Information delivery includes workshops, teaching pesticide re-certification courses, participation in various field days, and development of the Floriculture Web Page for Virginia.

Editor's Note: Washingtonpost.com moderators retain editorial control over Live Online discussions and choose the most relevant questions for guests and hosts; guests and hosts can decline to answer questions.

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Northern Virginia: Hello -- I am sure others will have a similar question to mine: how may cicadas affect plants and flowers (besides trees)? I live in a garden-style condominium complex and have quite a lot of plants and flowers on my balcony -- is there any reason to believe they may be at risk? Is there anything I might do to protect them? Thank you!

washingtonpost.com: You might want to read this wonderful piece from former Post gardening columnist Henry Mitchell, written the last time Brood X visited: The Cicadas, Bringing Their Sweet Symphony, (Post, May 1987)

Ed Lewis: Cicadas should not affect plants other than the small twigs of trees where they deposit their eggs. So, flowers will not be affected at all. There is no need to take any action to protect them.

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Washington, D.C.: In between emergences, do cicadas spend most of their underground time as eggs, or do they hatch and then spend that time as grubs? If the latter, how come they aren't found more often in the course of ordinary lawn planting or other digging?

Ed Lewis: Cicada adults deposit their eggs inside the small branches of trees, usually hardwoods. The eggs hatch there after 6 weeks or so and the nymphs fall to the ground and burrow to a depth of around 6-18 inches to begin feeding on roots. So their time underground is spent as a nymph. The reasons why we don't see them much by accident might be that they are deeper than we would usually dig to plant flowers or vegetables, they are associated with roots of hardwood trees (where we probably wouldn't plant anything anyway), and they are fairly small for most of their lives. They are common in the soil, but the odds of finding one digging are small.

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Texas: Dr. Lewis,

I have a general bug-related question. When I was a kid growing up in Arkansas, we would often see the "shells" of some sort of flying insects attached to tree trunks. Being kids, we would collect them. As best I can remember, the shells were about an inch long and brown.

Locally these critters were called "locusts." But I don't think they were the "biblical" style of locusts, which I seem to remember reading were what we would call grasshoppers. Were they cicadas?

I've wondered about this for years. Would appreciate any clarification.

Ed Lewis: Yes, these were probably cicadas. Or rather their cast off nymphal exoskeleton, which we entomologists call an exuvium. "Locust" is an inaccurate but often-used common name for all cicadas. I grew up in central New York State, and that's what we called them too.

You are also correct about what locusts really are. They are grasshoppers, and this term usually refers to the migratory locusts that devastate crops in sub-Saharan Africa.

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Chevy Chase, Md.: My daughters (ages 4 and 6) think the cicada emergence is just about the coolest thing that's ever happened. I know the bugs don't bite or sting, but I'm still mildly freaked out at the sight of the girls touching and picking up these insects. Are there any health/hygiene concerns about touching the cicadas?

Ed Lewis: I agree, these are really cool insects! In Blacksburg, last year was the big emergence, only the second one that I've ever seen. I have never heard of any health concerns associated with cicadas. I think that there is no reason to worry. If your daughters can hold on to them when they produce their song, I'm really impressed.

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Georgetown, Washington, D.C.: After the adults mate, what happens to them? Do they stay in the trees?

Ed Lewis: The adults mate and lay eggs pretty soon after they emerge from the ground. Their whole life span is usually from 2 to 4 weeks. They lay their eggs in batches of 1 to a few dozen per branch, and distribute their total of 400 to 500 eggs among several different branches. This activity takes most of their lives.

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Falls Church, Va.: is the emergence something of a bell curve -- is there a peak in their numbers and then a falling off? If so, what is the approximate timetable?

Ed Lewis: Most of the cicadas will emerge over a period of a few nights. There is certainly a peak, but the objective is for all of them to be around at the same time so they can find mates. The whole period when you will see the adults will last 4 to 6 weeks.

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Bladensburg, Md.: This question is from Ms. Dudley's 4th grade class at Rogers Heights Elementary School.

What do they eat? Will they bite for food?

Ed Lewis: Adult cicadas don't really eat very much at all. They just mate, lay their eggs and that's it.

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Bethesda, Md.: I just put up netting on two young trees I have (an oak and a cherry). How do the cicadas get on the trees? My neighbor thought they flew to the top, rather than crawl up the trunk from the bottom.

washingtonpost.com: I'd like to interject that they apparently do both. I netted some small viburnum bushes last week and there are now tons of trapped cicadas inside the netting.

Ed Lewis: They can indeed to both. If you put a net around a tree, and there are nymphal cicadas inside the perimeter of the net, they are likely to crawl up the tree to molt. They are also pretty good fliers and will fly from tree to tree, either to find mates or to lay eggs. If you want to protect the tree, just remove the net, shake off the cicadas and put it back.

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Falls Church, Va.: On our street I've noticed very local concentrations of cicadas, particularly around street light poles. Several poles are covered with them each morning, while nearby trees are essentially empty. The street in front of the poles is littered with the remains, while the street a few feet away is clean. Does the presence of the light attract the nymphs when they emerge or did it attract their egg-laying mother 17 years ago? (The poles are not next to trees, so the pole cannot have been the nearest vertical surface from the point of their emergence.)

Ed Lewis: When the cicada nymphs come up from underground they wander around until they find a vertical surface. They then climb up and molt. While they are feeding underground they don't move very much (at least we think they don't, I've never actually seen this documented anywhere). So this kind of distribution might reflect the distribution of eggs laid 17 years ago.

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Adelaide, Australia: When do you think the cycle will be finished, and could you give an estimate of when the Washington D.C. area should be free of cicadas?

Ed Lewis: The adults are around for 4-6 weeks. So, if they are just beginning now, I'd expect them to be gone by the end of June. Hurry and visit, you don't want to miss this!

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Arlington, Va.: Does anyone know how far cicadas eventually wander from their birthplace? It's clear that they fly in from your neighbor's yard, but how far away will they go? Not that I expect a yard with no cicadas -- I just wonder if the cicadas I will see buzzing in my yard were primarily born on my block, or do they like to move around?

Still none in our neighborhood. We have the little mounds and some holes under the trees, and our neighbors have assured us the place will be teeming with them, based on their 1987 experience.

Ed Lewis: This is a great question. I wish that I had an equally useful answer. I really don't know how far an adult moves in a life time. It is pretty difficult to conduct scientific research on something that is around for 4-6 weeks every 17 years.

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Bethesda, Md.: I have seen several contradictory write ups on Cicadas and their threat to pets. I have heard that they are filled with protein and won't hurt your animal if they were to eat one, but I have also heard that they can be harmful and to try your best to prevent your pet from eating them. Which theory is correct?

Ed Lewis: My friends around Blacksburg, where the emergence occurred last year, told me of their dogs "eating them like popcorn". As far as I know, all dogs have remained healthy and happy. No toxicity has been reported in the scientific literature either.

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Baltimore, Md.: What percentage of Brood X will emerge this year: exactly 100 percent? Or are there always some stragglers who show up the next year, or some who jumped the gun and emerged last year?

Ed Lewis: There is always some level of variability in biological systems. So, most, but not all, will emerge this year. There will be some stragglers, probably, but they will likely go unnoticed. Another note on variability here is that each brood is composed of 3 seperate species of cicada. So, even though they may all look the same to us, they look different to each other.

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Nashville, Tenn.: I just moved here 2 years ago and have yet to witness the cicada "invasion."

How bad does it really get? I have a feeling everyone here has just been trying to scare me with talks of cicadas "climbing up walls" and "flying into your face in swarms."

Thank you!

Ed Lewis: Well, I guess it depends on what you consider "bad". There are lots of insects all over the place, that's for sure. But, they make an interesting and furious sound, they don't really hurt anything or anyone and they are only here one time each 17 years. This is a rare and fascinating biological phenominon.

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Annandale, Va.: This is the first emergence that I've had interest in collecting the teneral (newly molted) adults for possible food. How long will I be able to find tenerals? Is it just the next couple of mornings and wait for another 17 years?

Also, I caught a few dozen nymphs last night and took them inside to molt -- kind of like watching popcorn pop in slow motion. Does it have to be dark for the nymphs to molt? It did seem that most of them "got around to it" once I turned off the main lights for the evening (I had set up various vertical surfaces in a big tray -- kind of an ad hoc fake tree).

Thanks!

Ed Lewis: Most of the teneral adults will be found within a few days. So, this will be a rare meal indeed. Of course, you can collect the annual or dog day cicadas each year if you really crave them. They are not as abundant, but they are bigger!

The nymphs do usually molt during the night. Great idea about the pan and vertical surfaces! That must have been interesting to watch.

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Bowie, Md.: Dr. Lewis
My class of 6th graders would like to keep some cicadas in our classroom. What should we put in the insect cage with them? Do they need water? Will they survive in a cpative environment? Any help would be appreciated.

Ed Lewis: I would put some water in a container with a small top. Then insert some cotton through the top into the water. That will be water that they can drink. They don't feed much, so they don't really need anything else. I don't know how they will do in captivity, but for a few days they should be OK in these conditions.

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Arlington, Va.: Tell me more about these cicada nymphs who will "drop from the trees" in, what, about four weeks? I mean, is it going to raining nymphs or what? Will it be all-clear to go back into the garden without getting a shirt-full of what I've heard described as "rice-grain-sized" bugs?

Ed Lewis: I wouldn't worry too much about a deluge of nymphs. One way to know where they will be dropping from is a characteristic damage caused by the egg laying called "flagging". This happens because when the females lay eggs, they slice open the bark of small tree branches and insert their eggs inside. This will cause the leaves on the branch tip to die, and you can see this damage readily. There is no danger to a large tree, it is just aesthetic.

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Chantilly, Va.: Why do they only appear every 17 years? And why only in a certain section of the U.S.?

Ed Lewis: There are some very interesting hypotheses about why only once in 17 years. Most of them have to do with avoiding predators or pathogens. If the adults are present at 17 year intervals, few predators, parasites or pathogens will become specialists at eating or infecting these insects. So that is one way to avoid natural enemies. Another strategy they can use is that there are just sooooo many of them around at the same time that proportion of the population that gets eaten is quite small, and many predators get confused when confronted with a sea or prey.

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Washington, D.C.: Brood X seem to be smaller and much more colorful than the annual cicadas I've encountered. Is that correct?

Ed Lewis: Yes, they are smaller than the annual cicadas. And, personally I find them much more appealing.

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Alexandria, Va.: What effect will the cicada invasion have on other insect species' populations? Specifically, can expect greater numbers of mosquitoes, bees, wasps and biting flies this year because birds and other predators have become sated on the easy-to-prey-upon cicadas?

washingtonpost.com: And what effect will it have on the bird population?

Ed Lewis: I don't know what if any impact the cicadas will have on other insect populations. I would expect a minimal effect, since they are only around for a very small part of the growing season. The birds, at least the ones that are big enough to eat a cicada should be "fat and happy" for a few weeks.

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Washington, D.C.: Can you tell me how to tell the difference between males and females?

Thanks!;

Ed Lewis: The easiest way is that males make the noise.

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Kensington, Md.: I'm fascinated with the idea that an organism of any sort can spend 17 years underground before its brief moment in the sun. Can you clear up a confusion I'm harboring though: does a given individual Brood-X cicada spend those 17 years feeding on roots in the dark, or is it a string of generations living underground before one lucky one gets to come topside? I gather the former, but no article I've seen has been literal enough to clarify this for me.

Assuming that it IS a single lifespan of 17 years, doesn't that make this species one of the longest-living of the animal kingdom? Aside from some mammals, a few birds and turtles (which still means a tiny percentage of all species), I can't think of any that live that long. And surely no insects -- or are cicadas insects? In any case these little guys strike me as rather humble when you consider the history they've "seen" (or not seen, being underground!).

Thanks for stopping in here to answer questions.

Ed Lewis: Each insect does indeed live for 17 years! This does make it an unusually long lived insect. I can't just off the top of my head think of one that lives longer. But, there are several insect species that live more than a single year; termite queens, honeybee queens, many scarab beetles, etc.

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Reston, Va.: Hello,

Are cicadas harmful to horses or dogs if injested? I know my dog will eat quite a few as he seeks out anything flying by. I understand he might have GI issues due to eating cicadas, is this true? My main concern is for my horses, they are prone to colic. I feel they may eat some by accident while grazing.

Thanks for your time.

Ed Lewis: Horses and dogs should be fine.

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Chevy Chase, Md.: My five-and-a-half-year-old daughter has the following question: How do the cicadas know to emerge after 17 years? What do they do in the other 16 years? How you ever eaten one?

Ed Lewis: These are tough ones. How they emerge at the same time has to do with an internal clock. They all develop at the same rate, and become adults at the same time. So, it isn't really a matter of "knowing" when to emerge, like a catterpillar doesn't "know" when to become a butterfly. They go through a series of developmental steps, which are programmed very tightly, then they emerge. During the other 16 years, they feed on roots in the ground.

I haven't eaten one, but one of the other participants has, if you've been following the conversation.

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Washington, D.C.: Are Cicada's a local phenomena, or are they going to be around the whole country?

Ed Lewis: They are common in the mid-atlantic and northeastern states. Other types of cicadas are found in other places. The broods are on differrent schedules, though, depending on where they are found. As I mentioned earlier, last year they emerged in Blacksburg.

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Washington, D.C.: How long do the cicadas stay around? Some reports say three weeks and some say six weeks and some say three months.

Thanks

Ed Lewis: The 17 year cicadas will be around until late June or early July. The annual cicadas will be around later in the summer, and perhaps the reports of cicadas lasting for months are just combining the different types.

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Portree, Isle of Skye, Scotland: I am rather thrilled to be visiting this area to witness such a rare and wondrous event! That being said, I would like to have my viewing pleasure limited to only the time I am actually outdoors.

How do we gently capture any interlopers who stray into an open door to the house, or even into our auto? I would not wish to harm them by picking them up incorrectly. Can they be harmed by handling them, even with care?

Ed Lewis: These are pretty sturdy insects. If you don't mind, just carefully picking them up in your hand and putting them outside should be fine. Or, you could sweep then into a box or some other container.

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Washington, D.C.: Apparently birds, squirrels and other animals eat many cicadas. Since the insects are so numerous, can we expect that the well fed animals will have large numbers of offspring?

Ed Lewis: Maybe they will have more offspring. But, most animal species that reproduce annually would not have much of an increase in reproduction based on a resource that is so ephemeral. If they were around for a few years, the answer would be very different, I suspect.

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Silver Spring, Md.: Cicadas survive for 17 years under the soil before they emerge. In the suburbs around the Washington area, where development has boomed for some time, there must be many areas where the soil has been completely torn up and re-landscaped since 1987. Will this impact Brood X in any way?

Ed Lewis: It may. Of course, if the nymphs are all of a sudden living underneath a parking lot, the impact is pretty significant. Also, if the various landscaping practices removed soil to a depth of 18 inches, the nymphs might have been killed in the act. Finally, if no hardwood trees are left, they will fly to where they can find them.

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