The Seventeen-Year Cicada
by EJ Landsman
But if [a cicada] happens to get into the insect net, it immediately announces its misfortune with a continuous damped piping, something like a spinning motor; if the cicada is held between one’s fingers, it keeps making the noise until it is released. Especially at such a time, one scarcely can avoid a feeling of great sympathy for the comic originality of this otherwise defenseless creature.
The periodical cicada’s life cycle is something of a paradox. An individual cicada’s transformation from egg to nymph to mature adult takes an astonishing seventeen years, but its adult life is over in a single summer. At every emergence some people inevitably react with revulsion and fear, despite the fact that, as Walter Linsenmaier notes above, cicadas are wholly defenseless—they neither bite nor sting. They don’t even pose a threat to crops, although we can thank Bob Dylan for perpetuating this false reputation with his song “Day of the Locusts,” written during the 1970 emergence of Brood X.
Magicicada is the genus encompassing all seventeen-year cicada species. Native to eastern North America, the cicadas emerge in a synchronous population of millions called a brood. Most broods include all Magicicada species. (Brood III, for example, will include the Magicicada septendecim, M. cassini, and M. septendecula, each with a slightly different appearance and song despite sharing an identical life cycle.) After climbing into a tree, the wingless nymphs molt and emerge from their exoskeletons as winged adults. Their next four to six weeks are spent singing, mating, laying eggs, and finally dying in such numbers that in some areas their bodies carpet the ground. About six weeks after the die-off, the eggs, laid in incisions in tree bark, hatch into nymphs, which drop and burrow into the ground. They remain underground, feeding on fluid from tree roots, for seventeen years—the longest gestational period of any known animal. After their nearly two-decades-long development, and according to some developmental cue scientists have yet to identify, the brood disinter themselves to molt and start the process over again.
Humans who have lived through a Magicicada emergence can tell you that a brood is a formidable presence, and one that often incites some panic. In fact there are a variety of websites created for the sole purpose of tracking brood emergences and disseminating important information about the cicadas—mainly that although large, loud, and overwhelmingly numerous, they don’t harm humans. You still might not want to host an large outdoor events during emergence years, as your celebration is liable to be disrupted by the sound their singing. Male cicadas will convene by the millions to sing together in a phenomenon called a chorus in an attempt to attract females. Although their numbers may be an impediment to the likelihood of any individual being selected by a female, the volume of their singing is a powerful repellant against predators. The sound of a chorus has been compared to the decibel level of a rock concert, and has been known to drive birds out of trees.
The cicada’s song is exceptional not only for its volume but for the mechanism by which it is produced. Whereas crickets and grasshoppers grate their legs together to produce their call, cicadas’ noise-making mechanism is not a bow-and-string construction, but a drum: a pair of resonant membranes within their bodies called tympana, which are vibrated by tiny attached muscles. Their whole physiology seems to be centered around these membranes: their internal structure is contorted, the digestive tract curled upon itself to make room for a resonating chamber that helps to amplify the sound of their calls. Thus the startling size of the individual cicada and the enormity of its sound are interconnected.
Brood X, the same one that inspired Bob Dylan, emerged again in May of 1987, right on time. The millions of chorusing males might have been one of the first sounds I ever heard, so it doesn’t surprise me that they still captivate me years later.