Cicada

Common Name: Cicada, Periodical cicada, 17-year Locust, Harvest fly – The common name cicada is from Latin meaning ‘tree cricket’ dating in usage from the 14th Century. In all probability it is in part onomatopoeia in reference to the sonorous noise produced by cicadas.

Scientific Name: Magicicada septendicum – The preternatural appearance of the cicada after an absence of seventeen years is so unusual as to seem to have an occult origination and therefore magical. The species name is Latin for seventeen to indicate the number of years in the cycle.

Potpourri: The emergence of up to 1.5 million cicadas per acre over an expansive area encompassing hundreds of square miles every 17 years is unique among the many curiosities of nature; the cacophony a crescendo to a long wait in darkened silence. The oversized and starkly red compound eyes that protrude ominously from the sides of a foreboding black head in combination with the mysterious ‘W’ embroidered near the trailing edge of the wing suggests Stygian origin. This is perhaps the etymology of the mistaken name locust, a type of grasshopper that swarms in scourging numbers bent on crop destruction so devastating as to evoke the biblical ‘plague of locusts.’ There are few events of nature which result in a perturbation so profound; the epitome of phenology, the study of natural phenomena that occur periodically.

Cicadas abound geographically due to their adaptable success in filling an ecological niche that protects them from predation with sufficient nutrition for growth and procreation. Species numbers vary according to reference, but there are about 3,000 individual cicada species worldwide of which 1,000 occur in the Western Hemisphere; mostly in tropical environments. The periodical cicadas are among the 180 species endemic to the United States and southern Canada. Cicadas are in the order Hemiptera (half-wing in Latin) known as the ‘true bugs’ and are differentiated taxonomically into a suborder Homoptera (same-wing) due to their characteristic membrane-thin wings held aesthetically in lengthwise alignment with the plump body. The homopterans include aphids, leafhoppers and spittlebugs. True bugs suck. They are grouped according to the evolution of mouth parts in a beak-like rostrum ideally suited for imbibing the liquefied contents of other organisms; the rostrum contains two mandibles for making a hole and two maxillae that form a tube for alternatively injecting digestive saliva and ingesting nutritive fluids. Cicada nutrition is derived from the xylem sap that flows in the roots of a host tree. [1]

As is the case with all arthropods of the Class Insecta, cicadas have a life cycle that metamorphoses at least in part. A post-coital female deposits 400 to 600 eggs in 40 to 50 different nests consisting of drilled slots in small branches about one half inch in diameter. The egg-laying may result in the death of the branch, known as “flagging.” The eggs hatch after about two months into ant-size larvae that fall to the ground and begin digging to access the tree root food source; their fore legs are especially adapted for digging. Burrow depth varies according to reference and possibly by species from about one foot to eight feet. This has apparently been an historical conundrum; Moses Bartram writing in 1767 notes “I have not yet been able to discover the full depth to which these little animals descend. Some, I have heard, have been found thirty feet deep. I myself have seen ten.” [2] It is quite possible that this variability is correct, and that they keep digging until they literally hit roots. For almost all cicadas, the subterranean sabbatical that lasts for a few years is punctuated by emergence from the deep and metamorphosing to adults. This occurs randomly in any given year toward midsummer; they are therefore sometimes called dog-day cicadas in reference to the period of the ecliptic cycle during which the Dog Star Sirius (the alpha star of the constellation Canis Major and the brightest in the night sky) is visible; Sirius is best seen in the starry nights of mid-winter January and not mid-summer July [3].  The periodical cicadas, meanwhile, are just settling in for the long haul.

There is considerable conjecture about the provenance of the 17 year cicada cycle even as there is no debate about its efficacy; the sheer number of progeny is proof of the latter. As the genus Magicicada is indigenous to eastern North America, there was no a priori knowledge of the phenomenon outside Native American experience until the European colonists geographically expanded and experienced its repetition. While their appearance in any given year could hardly be missed, the periodicity would not be noted for at least one and probably two cycles; what an average person would live to experience. Peter Kalm was sent by the Royal Swedish Academy to North America to study flora from 1748 to 1751; he recorded in the Swedish Transactions of 1756 “There is a kind of locusts which about every seventeenth year come hither in incredible numbers. They come out of the ground in the middle of May and make, for six weeks, such a noise in the trees and woods, that two persons that meet in such places, cannot understand each other.” The genus Magicicada was officially instated by his noted Swedish countryman Carolinus Linnaeus in 1758. But that was just the beginning of a century of observation and recordation necessary for a full understanding of the recondite life cycles of the periodical cicadas. The first noted anomaly was that some of the periodical cicadas have a life cycle of 13 years, an observation first documented in 1845 by D. Phares of Woodville, Mississippi in the Woodville Republican newspaper. It was not until 1907 with the publication of a USDA Bulletin by the government entomologist C. L. Marlatt entitled ‘The Periodical Cicada’ that the full range and scope of cicadas became manifest. Marlatt proposed thirty geographic groups called broods designated by Roman numerals I – XXX; seventeen broods of 17-year cicadas and thirteen of the 13-year variant. [4] The symmetry of the assignations was surely the result of apophenia, finding patterns in random data, as subsequent field evaluations established only 17 broods of which two have since become extinct; the original Roman numerals are still in use. As of now, there are twelve 17-year and three 13-year cicada broods, separated by both geographic location and by timewise sequencing. Brood X is the largest of the 15 extant groupings; known as the Great Eastern Brood, it covers areas in fifteen states that include the mid-Atlantic region. [5]

The phenology of the periodical cicada is a matter of scientific interest due to complex and multi-species interaction with different environmental factors; it is also a matter of public interest due to the auditory variance from the quotidian when they emerge. An entomologist at the Maryland Department of Agriculture measured the din of cicada mating calls in the mid – 90 decibel range, about the same as a lawn mower, noting that “it got to the point where your skin started to crawl”[6]. There are three different species of Magicicada designated decim, cassini and decula that independently evolved a 17-year life cycle and subsequently to the 13-year life cycle, the decim having done so twice. While cicada fossils date from the late Permian Period about 300 million years ago (mya), phylogenetic studies indicate the divergence of the periodical cicadas about 4 mya with subsequent branching in the intervening years to the extant seven species of Magicicada: the 17-year M. septendicum, M. septendecula, M. cassini; and the 13-year M. tredicum, M. neotredicum, M. tredecula and M. tredecassini. DNA studies completed in 2012 provided the first real scientific understanding of the transitions that occurred over the last four million years. The overarching hypothesis is that predator satiation and the glacial cycles of the Pleistocene Epoch were the forcing factors for population survival and geographic dispersion.

What prompted the original lengthening of the underground period from several years to seventeen is a matter of conjecture, but survival from predation would clearly be a key factor. The term predator satiation refers to the simultaneous emergence of so many individuals that predators become satiated so that there is a concomitant high rate of cicada survival; the long, prime number periodicity ensures against a cyclical predator multiplying to meet the food supply. The glacial cycles of the Pleistocene Epoch resulted in the formation of periodic areas of suitable habitat during the warmer interglacial periods; it is these glacial basins that coincide with the current boundaries of the periodical cicada broods. In other words, cicadas evolved independently to the 17-year cycle at least eight times to form the regional broods we they currently occupy, a phenomenon called convergent evolution. The different species individually adapted to the cyclic pattern of the original species thereby becoming synchronized to the same cycle. The subsequent divergence of the 13-year species occurred about 530,000 years ago when the southern M. tredicum diverged from the northern M. septendicum. The prevailing theory is that the warmer temperatures of the south during interglacial periods moved their emergence up by four years. It has been empirically established that a ground temperature of 64°F triggers cicada pupal ascent and this would occur consistently earlier to the south. [7]

Fully metamorphosed adult cicadas live for several weeks, the culmination of years of growth and survival punctuated by the primordial drive to create as many offspring as possible. The Sturm und Drang of over three hundred insects per square meter advertising their virility with lawn mower-like 90 decibel mating calls can only be experienced; words do not suffice. The mating call is produced by two specialized organs called tymbals that each consist of a thin membrane with transverse struts – something like a snare drum. The contraction of the struts inward creates a clicking noise that repeats with every cycle with the mostly hollow abdomen as the echo chamber at a rate of about 7,000 cycles per second or hertz (by comparison, the whine of a mosquito is 600 hertz). Physically, this is accomplished by having as many as 1,500 scolophores, the organs that attach the membrane to the rigid exoskeleton of the body; by comparison, moths have at most four scolophores. [8] Each species has its own signature sound so that the corresponding female can make her choice, presumably based on tonal quality; the sounds of the three 17-year cicada species have been characterized as the word ‘pharaoh,’ a rotating lawn sprinkler, and a sizzling skillet. Close scrutiny has revealed that the female’s acceptance signal is a ‘finger snap’ sound that is made within a half-second of the completion of the male’s song. It is not as dour as it seems, as the subsequent courtship can be of some duration, and, in the compressed grow-mate-die cycle, a male may wait for a female to mature, chasing off other suitors with an interference noise to mask out the intruder. Given the stentorian sound, it stands to reason that the cicada has a means of blocking its own ears. The French nature writer Jean-Henri Fabre was so incensed with the noise of cicadas that he came to the conclusion that they must be deaf. To test the hypotheses, he borrowed two field guns used for local celebrations and fired them under a cicada infested tree next to his house in full song; the cicadas were completely unaffected. This rather obscure experiment found life in the poetry of the Pulitzer Prize winning Richard Wilbur, who concluded his poem ‘Cicadas’ with:

This thin uncomprehended song it is
springs healing questions into binding air.
Fabre, by firing all the municipal cannon
under a piping tree, found out
cicadas cannot hear [9]

The periodical cicada is a long-lived insect that thrives in an underground Palladium where its many mammalian and avian predators cannot intercede. It emerges in finality as an adult only to take advantage of mobility and the full range of auditory and visual senses to find a mate and consummate a relationship. In the anthropocentric world of the epigeal, this short burst of activity constitutes its life, when in reality it is the other way around; from the ground up. However, understanding subterranean activities is impeded by access, and it was not until 1889 on the Washington D.C. grounds of the Department of Agriculture that Chief Entomologist C. L. Marlatt instituted a test that lasted until the adults emerged in 1906. Based on digging up various parts of the habitat over the 17 year test cycle, it was determined that the cicada larva molted four times until pupation and then an additional two times before the final adult metamorphosis. The total of six molts at intervals of two to three years was necessary to account for the growth of the larva and then the pupa; the most notable changes were the increasing complexity of the anterior legs, with enormous enlargement of the femora and tibia. In the opinion of Marlatt, these legs were specifically designed for “digging, tearing and transporting earth in the course of the insect’s subterranean life.” [10] It is the adaptation to a long life underground that is the sine qua non of the periodical cicada, and not its dystopian emergence after nearly two decades. The plump white cicadas that emerge from the last pupal shell are easy prey for birds until the predators are satiated; Melanism rapidly turns them black as camouflage against decimation.

Cicadas have figured prominently in folklore and fairy tale on a global scale. In ancient China, they were regarded as symbols of immortality in a manner similar to the deification of the scarab by the ancient Egyptians. Depictions of cicadas have been found on funerary vessels and carved bone spatulas dating from 1500 BCE. The symbolism of cicadas was persistent up to and including the Han Dynasty of 200 CE, their use having evolved to an amulet that was placed in the mouth as a part of the burial rite. Some studies have intimated the usage of similar jade cicada amulets by the Mayans and other Native American peoples suggesting some prehistorical cultural association that spanned the Pacific Ocean. The natural history of the cicada was metaphor for early Buddhist writings, the cast off carapace of the pupa in the metamorphosis to adult serving as a symbol of the hollow nature of human existence absent spiritualism. [11] Aesop’s classic Ant and the Grasshopper fable was originally written as the Ant and the Cicada. The storyline contrasts the diligent ant toiling to store food while the blithe cicada spends the entire summer singing. With the advent of winter, the starving cicada beseeches the ant and is rebuffed; the moral of hard work triumphing over idleness is a recurrent theme in Western Civilization. This was at one time much more prevalent in cultural associations than today. The late nineteenth century French artist Jules-Joseph Lefebvre named his painting that depicted a young, idle and artistically nude young woman among fallen leaves ‘La Cigale,’ the French word for cicada. That it was a metaphor for improvidence was implicit. [12]