By Krista Stracka ~
A few remarks upon Cicada septendecim will doubtless prove of interest now that the species has been occupying so much attention.
A peculiar sound has been droning from the treetops in parts of the Eastern and Midwestern states like a hovering alien spacecraft. We have again been invaded by trillions of the large, red-eyed creatures of Brood X—one of at least 15 broods of the 17-year periodical cicada (genus Magicicada). Since 2004, these beings have lived a subterranean (rather than extraterrestrial) existence and have emerged from the ground, clumsy but lovestruck, to metamorphize, breed, and lay the next generation over a period of four to six weeks.
There are over 3,000 species of cicada worldwide, but the seven species of the periodical cicada can only be found in eastern North America. Brood X (as in the Roman numeral 10) includes the three species of 17-year cicada (Magicicada septendecim, M. cassinii, and M. septendecula). Every seventeen years, a new generation crawls out from the dark, quiet earth like clockwork, offering yet another opportunity for scientists and the public alike to learn more about the incredible insect, including its songs—its loud, loud songs.
In 1633, William Bradford, governor of the Plymouth Colony, described the chorusing as a “constant yelling noise as made all the woods ring of them, and ready to deaf the hearers.” According to the NIH NIDCD’s It’s a Noisy Planet. Protect Their Hearing program, the songs used by the male cicadas to attract females can reach over 90 decibels—as loud as a motorcycle. Plug your ears!
The acoustic behavior of the cicada has captivated audiences for centuries. Aristotle recognized its mechanism for sound production differed from other insects but was not aware of the organ responsible for the function. Comparative anatomist Giulio Casseri (approximately 1552-1616) was the first to describe the sound-producing organs (tymbals) of the male cicada in his milestone work of comparative anatomy, though credit for the first accurate description of its mechanism is given to René-Antoine Ferchault de Réaumur for his six-volume pioneer work Memoires pour servir a l’histoire des insectes published almost 140 years later.
Early written accounts and scientific works in the eighteenth century that focused specifically on the North American periodical cicada note their large numbers and deafening noise. The writings of two principal authors on the periodical cicada in the nineteenth century are freely available online in the NLM Digital Collections: Nathaniel Potter and C.V. Riley.
Baltimore physician Nathaniel Potter first encountered the insect in 1783 and began to study them in 1817. Potter rejected the “modern” use of cicada and preferred to use the name “locust” in part to distinguish the species from the annual or “dog day” cicada. Joined by Gideon B. Smith during the 1834 emergence, Potter dissected and described the sound-producing organs of the periodical cicada with the aid of magnification. Unlike the European species studied by Réamur, the musical structure of the male Magicicada is visible from the outside. Their findings were published in the 27-page Notes on the Locusta.
Where Potter detailed the instrument but left off with an “imperfect” analysis of the periodical cicada’s songs (his own word), Charles V. Riley picked up during the emergence of 1885 in his The Song-notes of the Periodical Cicada. Riley is often recognized as the founder of modern entomology and was the first curator for the Smithsonian’s Insect Collection, now one of the largest entomological collections in the world. In this 4-page pamphlet, he carefully identified the three prevalent notes of the male Cicada septendecim on pages 2-4:
First, That ordinarily known as the phar-r-r-r-aoh note. This is the note most often heard during the early maturity of the male, and especially from isolated males or from limited numbers. It is variable in pitch and volume, according to the conditions just mentioned as generally affecting insect melodists….
Second, The loudest note, and the one which is undoubtedly most identified with the species in the popular mind, is what may be called the ‘screech.’ This is the note described by Fitch as “ represented by the letters tsh-e-e-E-E-E-E-E-e-ou, uttered continuously, and prolonged to a quarter or half a minute in length, the middle of the note being deafeningly shrill, loud and piercing to the ear, and its termination gradually lowered till the sound expires.” …This note is rarely made by solitary males, or when but few are gathered together….
Third, There is what may be called the intermittent, chirping sound, which consists of a series of from fifteen to thirty, but usually about twenty-two, sharp notes, sometimes double, lasting in the aggregate about five seconds. This sound is so much like that ordinarily produced by the barn or chimney swallow (Hirundo erythrogaster), that a description of the one would answer fairly well for both. It resembles also, though clearer and of higher pitch, the note of Microcentrum retinerve Burm [katydid]., which I have likened to the slow turning of a child’s wooden rattle highly pitched. [pages 2-4]
Both Potter and Riley compared the sounds of the songs to contemporary technologies that would have been familiar to 19th-century readers but may seem alien to some people today. For instance, Potter compared the sound of the “American songster” to the “scraping of a scissor grinder” (page 7). Riley likened the sounds to “a distant threshing-machine and a distant frog pond” (page 2). Modern comparisons to “a food blender spinning at top speed or a gas-powered lawn mower” would probably seem otherworldly to Potter and Riley, along with the electronic tools like hand-held decibel meters and slow motion videos now available to entomologists.
Observers of previous cycles have described feeling sad or nostalgic when the music of the cicada fades and the insects disappear. As amazing as this event has been to witness in 2021, many are eager for it to be over. While we wait for the next emergence of Brood X, we can ponder what technological changes seventeen years will bring and what will they sound like to us when this next generation rises to sing in 2038.