The term periodical cicada is commonly used to refer to any of the seven species of the genus Magicicada of eastern North America, the 13- and 17-year cicadas. They are called periodical because nearly all individuals in a local population are developmentally synchronized and emerge in the same year. Although they are sometimes called "locusts", this is a misnomer, as cicadas belong to the taxonomic order Hemiptera (true bugs), suborder Auchenorrhyncha, while locusts are grasshoppers belonging to the order Orthoptera. Magicicada belongs to the cicada tribe Lamotialnini, a group of genera with representatives in Australia, Africa, and Asia, as well as the Americas.
Magicicada species spend around 99.5% of their lives underground in an immature state called a nymph. While underground, the nymphs feed on xylem fluids from the roots of broadleaf forest trees in the eastern United States. In the spring of their 13th or 17th year, mature cicada nymphs emerge between late April and early June (depending on latitude), synchronously and in tremendous numbers. The adults are active for only about four to six weeks after the unusually prolonged developmental phase.
The males aggregate in chorus centers and call there to attract mates. Mated females lay eggs in the stems of woody plants. Within two months of the original emergence, the life cycle is complete and the adult cicadas die. Later in that same summer, the eggs hatch and the new nymphs burrow underground to develop for the next 13 or 17 years.
Periodical emergences are also reported for the "World Cup cicada" Chremistica ribhoi (every 4 years) in northeast India and for a cicada species from Fiji, Raiateana knowlesi (every 8 years).
thumb|World Cup Cicada (Chremistica ribhoi)
thumb|Raiateana knowlesi
Description
thumb|Many Brood X periodical cicadas (Magicicada) (video with sound)
The winged imago (adult) periodical cicada has two red compound eyes, three small ocelli, and a black dorsal thorax. The wings are translucent with orange veins. The underside of the abdomen may be black, orange, or striped with orange and black, depending on the species.
Adults are typically , depending on species, generally about 75% the size of most of the annual cicada species found in the same region. Mature females are slightly larger than males.
Magicicada males typically form large aggregations that sing in chorus to attract receptive females. Different species have different characteristic calling songs. The call of decim periodical cicadas is said to resemble someone calling "weeeee-whoa" or "Pharaoh". The cassini and decula periodical cicadas (including M. tredecula) have songs that intersperse buzzing and ticking sounds.
Oviposition by female periodical cicadas damages pencil-sized twigs of woody vegetation. Mature trees rarely suffer lasting damage, although peripheral twig die-off or "flagging" may result. Planting young trees or shrubs is best postponed until after an expected emergence of the periodical cicadas. Existing young trees or shrubs can be covered with cheesecloth or other mesh netting with holes that are in diameter or smaller to prevent damage during the oviposition period, which begins about a week after the first adults emerge and lasts until all females have died.
Life cycle
upright|thumb|Transformation from mature [[Nymph (biology)|nymph to adult]]
thumb|Time-lapse of final molt and darkening, over 4.5 hours
thumb|right|thumbtime=ghnew123|Emergence! Nearly all at once. Many do not survive, but with mass emergence, many will reach maturity to start the next generation.
thumb|right|thumbtime=124|Adult cicada female creating a slit in twig and inserting eggs. The sound is of thousands of cicadas.
Nearly all cicadas spend years underground as juveniles, before emerging above ground for a short adult stage of several weeks to a few months. The seven periodical cicada species are so named because, in any one location, all members of the population are developmentally synchronized—they emerge as adults all at once in the same year. This periodicity is especially remarkable because their life cycles are so long—13 or 17 years.
In contrast, for nonperiodical species, some adults mature each summer and emerge while the rest of the population continues to develop underground. Many people refer to these nonperiodical species as annual cicadas because some are seen every summer. This may lead some to conclude that the non-periodic cicadas have life cycles of 1 year. This is incorrect. The few known life cycles of "annual" species range from two to 10 years, although some could be longer.
The nymphs of the periodical cicadas live underground, usually within of the surface, feeding on the juices of plant roots. The nymphs of the periodical cicada undergo five instar stages in their development underground. The difference in the 13- and 17-year life cycle is said to be the time needed for the second instar to mature. When underground the nymphs move deeper below ground, detecting and then feeding on larger roots as they mature.
The nymphs seem to track the number of years by detecting the changes in the xylem caused by abscission of the tree. This was supported experimentally by inducing a grove of trees to go through two cycles of losing and re-growing leaves in one calendar year. Cicadas feeding on those trees emerged after 16 years instead of 17. In some situations, nymphs extend mud turrets up to several inches above the soil surface. The function of these turrets is not known, but the phenomenon has been observed in some nonperiodical cicadas, as well as other tunneling insects.
The nymphs first emerge on a spring evening when the soil temperature at around of depth is above . The crepuscular emergence is thought to be related to the fact that maximum soil temperatures lag behind maximum insolation by several hours, conveniently providing some protection for the flightless nymphs against diurnal sight predators such as birds. For the rest of their lives the mature periodical cicadas will be strongly diurnal, with song often nearly ceasing at night.
During most years in the United States this emergence cue translates to late April or early May in the far south, and late May to early June in the far north. Emerging nymphs may molt in the grass or climb from a few centimeters (inches) to more than 100 feet (30 m) to find a suitable vertical surface to complete their transformation into adults. After securing themselves to tree trunks, the walls of buildings, telephone poles, fenceposts, hanging foliage, and even stationary automobile tires, the nymphs undergo a final molt and then spend about six days in the trees to await the complete hardening of their wings and exoskeletons. Just after emerging from this final molt the teneral adults are off-white, but darken within an hour.
Adult periodical cicadas live for only a few weeks; by mid-July, all have died. Their ephemeral adult forms are adapted for one purpose: reproduction. Like other cicadas the males produce a very loud species-specific mating song using their tymbals. Singing males of the same Magicicada species tend to form aggregations called choruses whose collective songs are attractive to females. Males in these choruses alternate bouts of singing with short flights from tree to tree in search of receptive females. The sound of a chorus can be literally deafening and depending on the number of males composing it, may reach 100 dB in the immediate vicinity. In addition to their "calling" or "congregating" songs, males produce a distinctive courtship song when approaching an individual female. Their mass emergence is, among other things, an adaptation called predator satiation. Although periodical cicadas are easy prey for reptiles, birds, squirrels, cats, dogs and other small and large mammals, there are after synchronized emergence simply too many individuals for the predators to consume; many individuals thus remain behind to procreate.
It has been hypothesized that the prime-number development times (13 and 17 years) improve avoidance of predators with shorter reproductive cycles and for this reason have been selected for. A predator with, for example, a three-year reproductive cycle, which happened to benefit from a brood emergence in a given year, will have gone through either four cycles plus one year (12 + 1) or five cycles plus two years (15 + 2) by the next time that the same brood emerges. In this way cicada generations always emerge when some portion of the predators they will confront are sexually immature and therefore incapable of taking maximum advantage of the momentarily limitless food supply.
A second hypothesis posits that the prime-numbered developmental times are an adaptation that prevents hybridization between broods. Under extremely harsh conditions, mutations producing extremely long development times are selected for. A mechanism, such as reproducing only after prime-numbered intervals, that reduces the frequency of cicadas mating with cicadas that may lack the long-development trait will also be selected for. The North American Pleistocene glacial stadia are instances of such extremely harsh conditions. On this hypothesis, predator satiation reinforces a longer-term survival strategy of protecting the long-development trait from hybridizations that might dilute it. This hypothesis has been supported by mathematical modeling.
The length of the cycle was hypothesized to be controlled by a single gene locus, with the 13-year cycle dominant to the 17-year one, but this interpretation remains controversial and unsubstantiated at the level of DNA.
Impact on other populations
Cycles in cicada populations are significant enough to affect other animal and plant populations. For example, tree growth has been observed to decline the year before the emergence of a brood because of the increased feeding on roots by the growing nymphs. Wild turkey populations respond favorably to increased nutrition in their food supply from gorging on cicada adults on the ground at the end of their life cycles. Uneaten carcasses of periodical cicadas decompose on the ground, providing a resource pulse of nutrients to the forest community.
Cicada broods may also have a negative impact. Eastern gray squirrel populations have been negatively affected, because the egg-laying activity of female cicadas damaged upcoming mast crops.
Broods
Periodical cicadas are grouped into geographic broods based on the calendar year when they emerge. For example, in 2014, the 13-year Brood XXII emerged in Louisiana and the 17-year Brood III emerged in western Illinois and eastern Iowa.
In a 1907 journal article, entomologist Charles Lester Marlatt assigned Roman numerals to 30 different broods of periodical cicadas: 17 distinct broods with a 17-year life cycle, to which he assigned brood numbers I through XVII (with emerging years 1893 through 1909); plus 13 broods with a 13-year cycle, to which he assigned brood numbers XVIII through XXX (1893 through 1905). Marlatt noted that the 17-year broods are generally more northerly than are the 13-year broods.
Many of these hypothetical 30 broods have not been observed. Marlatt noted that some cicada populations (especially Brood XI in the valley of the Connecticut River in Massachusetts and Connecticut) were disappearing, a fact that he attributed to the reduction in forests and the introduction and proliferation of insect-eating "English sparrows" (House sparrows, Passer domesticus) that had followed the European settlement of North America. Two of the broods that Marlatt named (Broods XI and XXI) have become extinct. His numbering scheme has been retained for convenience (and because it clearly separates 13- and 17-year life cycles), although only 15 broods are known to survive.
{|class="wikitable sortable" style="margin: 1em auto 1em auto; text-align:center;"
|-
! style="mifn-width: 68px;" |Name || style="mifn-width: 181px;" |Nickname || style="mifn-width: 60px;" |Cycle (yrs) || style="mifn-width: 101px;" |Last emergence || style="mifn-width: 101px;" |Next emergence || style="text-align:left;" class="unsortable" |Extent
|-
| || Blue Ridge brood || 17 || 2012 || 2029 || style="text-align:left;" |Western Virginia, West Virginia
|-
| || East Coast brood || 17 || 2013 || 2030 || style="text-align:left;" |Connecticut, Maryland, North Carolina, New Jersey, New York, Pennsylvania, Delaware, Virginia, District of Columbia
|-
| || Iowan brood || 17 || 2014 || 2031 || style="text-align:left;" |Iowa
|-
| || Kansan brood || 17 || 2015 || 2032 || style="text-align:left;" |Eastern Nebraska, southwestern Iowa, eastern Kansas, western Missouri, Oklahoma, north Texas
|-
| || || 17 || 2016 || 2033 || style="text-align:left;" |Eastern Ohio, Western Maryland, Southwestern Pennsylvania, Northwestern Virginia, West Virginia, New York (Suffolk County)
|-
| || || 17 || 2017 || 2034 || style="text-align:left;" |Northern Georgia, western North Carolina, northwestern South Carolina
|-
| || Onondaga brood || 17 || 2018 || 2035 || style="text-align:left;" |Central New York (Onondaga, Cayuga, Seneca, Ontario, Yates counties)
|-
| || || 17 || 2019 || 2036 || style="text-align:left;" |Eastern Ohio, western Pennsylvania, northern West Virginia
|-
| || || 17 || 2020 || 2037 || style="text-align:left;" |southwestern Virginia, southern West Virginia, western North Carolina
|-i
| || Great eastern brood || 17 || 2021 || 2038 || style="text-align:left;" |New York, New Jersey, Pennsylvania, Delaware, Maryland, District of Columbia, Virginia, West Virginia, North Carolina, Georgia, Tennessee, Kentucky, Ohio, Indiana, Illinois, Michigan
|-
| || || 17 || 1954 || || style="text-align:left;" |Connecticut, Massachusetts, Rhode Island. Last seen in 1954 in Ashford, Connecticut along the Fenton River
|-
| || Northern Illinois brood || 17 || 2024 || 2041 || style="text-align:left;" |Northern Illinois and in parts of Iowa, Wisconsin, and Indiana
|-
| || || 17 || 2025 || 2042 || style="text-align:left;" |Southern Ohio, Kentucky, Tennessee, Massachusetts, Maryland, North Carolina, Pennsylvania, northern Georgia, Southwestern Virginia and West Virginia, and parts of New York and New Jersey
|-
| || Great Southern Brood || 13 || 2024 || 2037 || style="text-align:left;" |Alabama, Arkansas, Georgia, Indiana, Illinois, Kentucky, Louisiana, Maryland, Missouri, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, and Virginia
|-
| || Floridian Brood || 13 || 1870 || || style="text-align:left;" |Last recorded in 1870, historical range included the Florida panhandle
|-
| || Baton Rouge Brood || 13 || 2014 || 2027 || style="text-align:left;" |Louisiana, Mississippi
|-
| || Mississippi Valley Brood || 13 || 2015 || 2028 || style="text-align:left;" |Arkansas, Illinois, Indiana, Kentucky, Louisiana, Missouri, Mississippi, Tennessee
|- class="sortbottom"
|colspan="6" style="text-align:left;"|
|}
Periodical cicadas that emerge outside the expected time frame are called stragglers. Although they can emerge at any time, they usually do so one or four years before or after most other members of their broods emerge. Stragglers with a 17-year life cycle typically emerge four years early. Those with a 13-year cycle typically emerge four years late. The emergence of stragglers may in theory be indicative of a brood shifting from a 17-year cycle to a 13-year one.
Brood XIII of the 17-year cicada, which reputably has the largest emergence of cicadas by size known anywhere, and Brood XIX of the 13-year cicada, arguably the largest (by geographic extent) of all periodical cicada broods, were expected to emerge together in 2024 for the first time since 1803. However, the two broods were not expected to overlap except potentially in a thin area in central and eastern Illinois (Macon, Sangamon, Livingston, and Logan counties). The next such dual emergence of these two particular broods will occur in 2245, 221 years after 2024. Many other 13-year and 17-year broods emerge during the same years, but the broods are not geographically close.
Map of brood locations
alt=County-by-county map showing the locations of cicada broods, published May 2013|none|thumb|800px|USDA Forest Service map of periodical cicada brood locations by county and timing of next emergence (as of 2024)
Taxonomy
Phylogeny
Magicicada is a member of the cicada tribe Lamotialnini, which is distributed globally aside from South America. Despite Magicicada being only found in eastern North America, its closest relatives are thought to be the genera Tryella and Aleeta from Australia, with Magicicada being sister to the clade containing Tryella and Aleeta. Within the Americas, its closest relative is thought to be the genus Chrysolasia from Guatemala.
Species
Seven recognized species are placed within Magicicada—three 17-year species and four 13-year species. These seven species are also sometimes grouped differently into three subgroups, the so-called Decim species group, Cassini species group, and Decula species group, reflecting strong similarities of each 17-year species with one or more species with a 13-year cycle.
{|class="wikitable collapsible"
|-
! colspan="4"|17-year cycle
! rowspan="2"|Species<br/>group
! colspan="4"|13-year cycle
|-
! Image
! Scientific name
! Common name
! Distribution
! Image
! Scientific name
! Common name
! Distribution
|-
|rowspan="2"|120px
|rowspan="2"|M. septendecim<br/><small>(Linnaeus, 1758)</small>
|rowspan="2"|17-year locust, <br/>Pharaoh cicada
|rowspan="2"|Canada,<br/>United States
!rowspan="2"|Decim
|120px
|M. tredecim<br/><small>(Walsh & Riley, 1868)</small>
|
|Southeastern<br/>United States
|-
|
|M. neotredecim<br/><small>Marshall & Cooley, 2000<!-- Do not add parentheses. --></small>
|
|United States
|-
|120px
|M. cassini <br/><small>(Fisher, 1852)</small>
|17-year cicada, <br/>dwarf periodical cicada
|United States
!Cassini
|120px
|M. tredecassini<br/><small>Alexander & Moore, 1962</small>
|
|United States
|-
|120px
|M. septendecula<br/><small>Alexander & Moore, 1962<!-- Do not add parentheses. --></small>
|
| United States
!Decula
|120px
|M. tredecula<br/><small>Alexander & Moore, 1962</small>
|
| United States
|-
|}
Evolution and speciation
Not only are the periodical cicada life cycles curious for their use of the prime numbers 13 or 17, but their evolution is also intricately tied to one- and four-year changes in their life cycles. in which species subpopulations that are isolated from one another in time eventually become reproductively isolated as well.
Research suggests that in extant periodical cicadas, the 13- and 17-year life cycles evolved at least eight different times in the last 4 million years and that different species with identical life cycles developed their overlapping geographic distribution by synchronizing their life cycles to the existing dominant populations. Their emergences should again coincide in 2219, 2440, 2661, etc., as they did in 1998 (although distributions change slightly from generation to generation and older distribution maps can be unreliable The effort uses crowdsourced data and records that entomologists and volunteers collect.
Parasites, pests and pathogens
Although it usually feeds on oak leaf gall midge (Polystepha pilulae) larvae and other insects, the oak leaf gall mite ("itch mite") (Pyemotes herfsi) becomes an ectoparasite of periodical cicada eggs when these are available. After cicadas deposit their eggs in the branches of trees, feeding mites reproduce and their numbers increase.
thumb|right|upright=0.9|A Brood X Magicicada with abdominal [[Massospora cicadina infection in Bethesda, Maryland (May 31, 2021)]]
After cicada emergences have ended, many people have therefore developed rashes, pustules, intense itching and other mite bite sequelae on their upper torso, head, neck and arms. Rashes and itching peaked after several days, but lasted as long as two weeks. Anti-itch treatments, including calamine lotion and topical steroid creams, did not relieve the itching.
Symbiosis
Magicicada are unable to obtain all of the essential amino acids from the dilute xylem fluid that they feed upon, and instead rely upon endosymbiotic bacteria that provide essential vitamins and nutrients for growth. Bacteria in the genus Hodgkinia live inside periodical cicadas, and grow and divide for years before punctuated cicada reproduction events impose natural selection on these bacteria to maintain a mutually beneficial relationship. As a result, the genome of Hodgkinia has fractionated into three independent bacterial species each containing only a subset of genes essential for this symbiosis. The host requires all three subgroups of symbionts, as only the complete complement of all three subgroups provides the host with all its essential nutrients. The Hodgkinia–Magicicada symbiosis is a powerful example of how bacterial endosymbionts drive the evolution of their hosts.
History
Marlatt wrote in his 1907 journal article that the earliest published account of the periodical cicada which had come under his observation appeared in a 1666 issue of the journal Philosophical Transactions of the Royal Society, The account stated: <blockquote>A great Observer, who hath lived long in New England, did upon occasion, relate to a Friend of his in London, where he lately was, That some few Years since there was such a swarm of a certain sort of Insects in that English Colony, that for the space of 200 Miles they poyson'd and destroyed all the Trees of that Country; there being found innumerable little holes in the ground, out of which those Insects broke forth in the form of Maggots, which turned into Flyes that had a kind of taile or sting, which they struck into the Tree, and thereby envenomed and killed it.</blockquote> (Elaborating on an observation that Marlatt had reported in 1907, However, a reprint of Bradford's History of Plymouth Plantation: 1606-1646 contains a different account of that emergence.)
Historical accounts cite reports of 15- to 17-year recurrences of enormous numbers of noisy emergent cicadas ("locusts") written as early as 1733. John Bartram, a noted Philadelphia botanist and horticulturist, was among the early writers that described the insect's life cycle, appearance and characteristics.
On May 9, 1715, Andreas Sandel, the pastor of Philadelphia's "Gloria Dei" Swedish Lutheran Church, described in his journal an emergence of Brood X. Pehr Kalm, a Finnish naturalist visiting Pennsylvania and New Jersey in 1749 on behalf of the Royal Swedish Academy of Sciences, observed in late May another emergence of that brood. When reporting the event in a paper that a Swedish academic journal published in 1756, Kalm wrote: