As I examined the map and zoomed in closer to the Philadelphia region, it was obvious. There was a big empty place on the map that mostly outlined Philly. The map I was looking at was one showing where Brood X of the 17-year cicadas (also called periodical cicadas) had been recorded in previous years and likely would appear this year.
The map, generated by John Cooley, PhD, is based on more than 45 years of field work by Chris Simon and Cooley and also specimen records in museum collections including those of the Academy of Natural Sciences of Drexel University where I work. It was clear from the map that this emergence, with all its hype, would not include Philadelphia!”
I have worked with museum specimen data for the last four decades as a collection-based scientist studying the diversity of insects. Museum specimens offer a rich resource of knowledge: what a species looks like, where it is found and when, what constitutes its genetic makeup, and other species associated with it. Also, a specimen with its collection labels offers a history of human endeavor – the place it was found, the time, and the collector who secured the insect. But what does an absence of specimens mean?
When I looked at the map again and that big bare area over Philadelphia, I had to think: what does it mean? Is it a real absence or just an artifact of incomplete sampling? Incomplete sampling seemed unlikely, as the American Entomological Society was established in 1859 in Philadelphia and continues today as the oldest entomological society in North America. There has been a strong presence of society members interested in insects and collecting specimens for over 160 years, all throughout the region.
Ok, I thought, perhaps the periodical cicadas had occurred here but were extirpated (made locally extinct) by the development of the city with its buildings and streets and pollution and loss of woodlands, etc. Other insects did disappear from the city, like the Regal Fritillary butterfly. A lot can happen in 17 years when you are living underground, right?
But the map also showed that Brood X was abundant in the Baltimore-Washington D.C. area. I remember driving in downtown Washington during the cicada emergence in 2004 and seeing periodical cicadas buzzing along the streets and across I-95 Philadelphia was also proactive in the 1800s protecting watersheds in the city to ensure clean water for its residents before a lot of that development had occurred, and that protection extended to the watershed forests – now our Fairmount Park system. So the forests are here to support the cicadas, even today. So cicadas should be here, if they ever were.
So maybe the hole in the map represents a true absence – the cicadas just aren’t in Philadelphia. Reasons unknown. But before I got too far down that path of thinking, my colleague at the Academy, Greg Cowper, sent me a photo of a pair of specimens in our collection, with the handwritten label “Phila. Pa. 6/16/02”!
It was a male and a female on the same pin, usually indicating, in entomologist parlance, that it was a pair found in copula, or mating. And interpreting the label date, it appeared the specimens were taken on June 16, 1902, nearly 120 years ago. Since it was the only specimen we had from Philly, I had to think: how reliable was it in showing that these cicadas really were in Philadelphia?
Occasionally specimens get mislabeled, but we don’t expect to see that when someone has handwritten the label on the specimen they collected. Could it be a specimen that hitched a ride on a cart into the city from someplace where we know periodical cicadas are found, such as Haverford? Sure, it happens, but the fact that this was a mating pair suggested to me that the person sampled a reproducing population, and not a stray from another area.
With that, I felt I had good reason to accept the record and to wonder where in the diversity of locales that make up Philly did these specimens come from? Since the specimens came with limited information, I thought perhaps there were some historical accounts on the cicada emergences that might help. So I started down the rabbit hole many of us do when so much information on the internet is so readily available – and what a rabbit hole (or cicada burrow) it led me down!
Although periodical cicada emergences were well known to the indigenous peoples in eastern North America, according to accounts from early European settlers, we don’t have any reports in written documentation for the Philadelphia region until the 1700s. In searching, I found a wonderful account John Bartram wrote in 1749 (also a Brood X year) about a mass emergence of periodical cicadas beginning in May “in the neighbourhood of Philadelphia.” He noted that “now there is a continual noise all over our woods and orchards, from morning to evening.”
A hundred years later, in an 1851 account, John Cassin, a well-known ornithologist at the Academy of Natural Sciences, described a mass emergence again in “this neighborhood especially in the woods at Powelton during the present year. I saw them in Delaware county Pennsylvania in 1834.” (also a Brood X year) Cassin noted that two species were present, one that was described by Linnaeus nearly a century before as Cicada septendecim, and a smaller species with a different song.
That second species was described as new by one of Cassin’s colleagues and named for him, Cicada cassini. Cassin noted this second species was abundant in Powelton in an orchard of apple trees in the most elevated part of the estate and also in trees in the adjacent woods. Cassin goes on to note that the periodical cicadas were noted “in this neighborhood” in May 1715 in early Swedish settler accounts.
I was perplexed by the “neighborhood of Philadelphia” remarks from both Bartram and Cassin.But then I realized that in Bartram’s time, his farm, sitting across the Schuylkill River was not part of Philadelphia proper; and even Powelton, which Cassin mentioned, was not part of the city of Philadelphia until 1854.
So periodical cicadas did occur in Philadelphia at least up until 1902. They were noted at Bartram’s farm, now Bartram’s Garden, and in the Powelton area, both in west Philadelphia. They apparently occurred in Delaware County, although we have no specific records. Are they still there? Are they in other areas of Philadelphia as well? This is the year to find out!
We have great tools to help us – smartphones with camera, video and GPS capabilities. We have fantastic apps and websites to record our observations such as iNaturalist, Bugguide.net and CicadaSafari. We can take a sample of specimens for the Academy’s collection to document the species presence now and allow others in the distant future to study them.Most importantly, instead of a limited number of “specialists” doing the observations, the tools allow a multitude of people of diverse backgrounds across the city to contribute their observations.
With the discovery of any still living populations of periodical cicadas within Philadelphia, we can take steps to preserve this wonderful natural phenomenon for future generations. But first we must see if they still do occur here.
Right now in April, we can look for the nymphal cicada exit holes appearing in the forest floor as these young cicadas await the right soil temperature to make their exit and transform into adults. We can listen for the cicada chorusing in May and June and zone in to see if one, two or three cicada species are present.
Some great places to start would be sites in West Philadelphia along the Schuylkill, such as Bartram’s Garden, The Woodlands, or even in Powelton Village. We need to check the city’s extensive Fairmount Park system, and maybe even Laurel Hill Cemetery where John Cassin is buried. Wouldn’t that be wonderful to hear a choir of Magicicada cassini singing their buzzing chorus over his headstone? Happy hunting!
Text and images by Jon Gelhaus, PhD, Curator of Entomology at the Academy of Natural Sciences of Drexel University and professor, Biodiversity, Earth and Environmental Sciences
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