Cicadas, Commencement and Citizen Science

A periodical cicada.
Photo: Marten Edwards

Before we know it, many of us in the Lehigh Valley will be sharing our parks, roadways, and gardens with Brood II 17-year periodical cicadas.  They are different from the green annual cicadas that we look forward to each July. Periodical cicadas have black bodies, orange wings, and red eyes. Unlike annual cicadas, they only reveal themselves in vast numbers every seventeen years. Their numerically rich and audibly famous lifestyles can be explored with a wealth of information at Cicada Mania and Cicada Central

Anna checking the ground temperature

The Lehigh Valley is home to all three species of 17-year cicadas. They belong to an exclusive clique of periodical cicadas, scientifically known as the Magicicada.  Magicicada are native to the Eastern United States and nowhere else in the world. When it’s time to leave their subterranean homes, all three species will dig out simultaneously. There is also a band of four closely related 13-year Magicicada species. The 13-year cicadas prefer the Southern states and are not found in Pennsylvania.

Periodical cicadas have no way to protect themselves beyond their sheer numbers. They cannot bite or sting and are apparently rather tasty due to a lack of defensive chemicals. Predators simply cannot eat enough of them.  Right after they emerge from the ground and molt for the last time, their bodies are soft and squishy. Their wings are not rigid enough for flight and the male sound-producing structures are silent. Since newbie adults (tenerals) are especially vulnerable to attack during their first tender hours, they tend to emerge after sunset. This way, they have all night to toughen up and start to fly before the birds, squirrels, and dogs start to feast on them. It takes about 4 to 6 days for adult males to achieve the level of maturity required to make their joyful noise.  Fortunately, their obstreperous pleas for female companionship are only made in the light of day, so they should not keep you up at night.  

Where and when they going to come out here in the Lehigh Valley? Short answer: nobody knows. It turns out to be a harder question than I would have expected. Surprisingly, the maps that show where periodical cicadas are expected come out in a given year are largely based on the spotty and sparse records that were available to Charles Marlatt, a USDA entomologist, back in 1923. He came up with the Roman numeral system to identify the group, or “brood” of cicadas that comes up each year, generally in a different place. 

Our natural environment has changed quite a bit since 1923. Forests have been cleared of trees and their cicada-laden roots for lumber, agriculture and strip malls.  Meanwhile, many of our pre-1923 farms have been returned to woodlands or transmogrified into housing developments. Suburban habitats can be either cicada-friendly or cicada-hostile, depending on landscaping and pesticide choices. Some Magicicada populations have certainly shrunk or gone extinct since 1923. On the flip side, it’s possible that some local populations have expanded their stomping grounds. 

I am not aware of any scientifically collected historical records of Brood II cicadas in the Lehigh Valley. This doesn’t mean they weren’t here back in 1996, 1979, 1962, 1945 and so-on back to the last ice age around 20,000 years ago.  It just means that they were not reported and verified by leading cicada researchers, such as Chris Simon at the University of Connecticut.  Her team recently investigated the genetics of periodical cicadas.  Their data suggest that Magicicada populations have been throwing their 17 or 13-year underground sap-sipping slumber parties for at least 3.9 million years.

Periodical cicadas were spotted in 1996 around Bear Creek Ski Resort.  A 1996 Morning Call article quoted cicada expert Chris Simon that back in 1979, Brood II cicadas emerged on “June 3 from Schuylkill Haven to Upper Mount Bethel Township.”  In 2008, brood XIV cicadas were observed in Bear Gap PA on May 25.  In a 2004 study of Ohio’s Brood X cicadas, the first emergence observations were made on May 9 and most had come out of the ground by May 14, a week earlier than historical records would have predicted.

Variations in local weather can jiggle the actual dates of emergence back and forth by about a week.  Checking the Lehigh Valley monthly average temperatures since 1948, this past winter doesn’t seem too far out of the ordinary.  NOAA predicts a warmer than usual April for this region.  I might err a little on the early side if I were placing a bet on this year’s Brood II emergence date.

Back in 2004, I got involved with mapping Pennsylvania’s periodical cicadas when Muhlenberg College asked me if the cicadas were going to ruin our commencement ceremony. Of course, I thought that cicadas would only add sparkle to the day, but it wasn’t an idle concern.  On June 9, 1970, Bob Dylan was upstaged and outperformed by Brood X cicadas while being awarded an honorary degree in Music from Princeton University.  This experience was immortalized in the lyrics to his song “Day of the Locusts” and the event was vividly recalled in the Daily Princetonian

This year, college commencement ceremonies in the Lehigh Valley are planned between May 4 (Penn State Lehigh Valley) and May 25 (Lafayette College).  Based on our limited historical data, we might expect to see cicadas emerge between May 25 and June 6, if we see them at all.  It takes another 4 to 6 days before they start to get noisy.  My guess is that all of the Lehigh Valley commencement ceremonies are going to be simply marvelous, even without the cicadas.

A popular “factoid” about periodical cicadas is that they emerge when the ground temperature is 64 degrees. On the grand scale, this is a reasonable rule of thumb. Northern populations emerge later than southern populations.  However, any patch of ground will have peaks and valleys, sunny and shady spots and other features leading to local variations in soil temperature.  Still, the vast majority of the Magicicada within an area will typically emerge after sunset within a few days of each other.  Clearly, some speedy developers wait for the slowpokes to get ready.  How do they decide which night to come out?  Twitter? 

There are at least two easy and fun ways that you can get involved in cicada citizen science yourself. The first project will is something you can try right now before you see or hear a single cicada. All you need is a mercury-free thermometer that is at least eight inches long.  Dash outside and poke it eight inches into the ground and measure the soil temperature. (A perfectly adequate soil thermometer can cost less than ten dollars.) When you have recorded the soil temperature, report it on Cicada Tracker. This experimental project is not intended to be a foolproof predictor of when and where the cicadas will actually emerge.  Nevertheless, it’s the first time that soil temperatures will be crowdsourced via the information superhighway.  Something new and interesting is bound to be discovered.

A significant way that everyone can participate in a scientific study of Brood II cicadas is through Cicada Central.  All you need to do is go to the site and report whether or not you see or hear cicadas at a specific location.  It is just as important to report if you do not find cicadas since this helps determine the margins of their range.  

Periodical cicadas are not just delightfully entertaining.  Their distributions can serve as long-term barometers of environmental health.  Cicada Central will improve the resolution of our current Brood II 17-year cicada maps.  Better maps will allow us to see how the cicadas are doing next time they make their above-ground cameos 2030 and beyond.

This mapping project is the brainchild John Cooley, a cicada scholar who has worked with Chris Simon and other cicada luminaries.  Dr. Cooley got hooked on cicadas as an undergraduate researcher at Yale University.  His citizen mapping efforts were given a major boost with a grant from the National Geographic Society.  The project has already contributed to national maps of 2004 Brood X and 2008 Brood XIV cicada emergences, which have set the standard for this kind of research.  Even the most dedicated team of professional cicada researchers would not be able to gather as much data as the thousands of people in our community who care about cicadas and the environment.  Please spread the word about this citizen-science opportunity to your family, friends, and neighbors.

This summer I will be joined by Muhlenberg College undergraduate researchers to supplement the Cicada Central database.  We will determine which species are present in the mix in specific locations and try to get a better handle on the local Brood II boundaries.  From a distance, the different bugs can be hard to distinguish by their looks.  Fortunately, the species are easy to tell apart by the distinct mating calls that the males exclaim with such gusto.

If you remember seeing cicadas in the Lehigh Valley back in 1996, 1979 or intervals of 17 years earlier, please post a comment and share your experience with us here!  When I get wind of the first signs of Brood II in this area, I will update to this blog and send a reminder to electronically celebrate your local cicada situation with a report to Cicada Central.  

This work by Marten Edwards is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

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