Periodical Cicadas ("The 13-Year Locusts")
Periodical Cicadas1 (“The 13-Year Locusts”)
L.L. Hyche, Associate Professor
Department of Entomology
Once every 13 years, precisely on schedule, there occurs in widely scattered areas of Alabama woodlands a remarkable historic and spectacular entomological event. Peaceful wooded areas are transformed literally overnight into amazing scenes of noisy insect activity. Lower portions of tree trunks, and stems, twigs, and leaves of understory plants are littered with tan to brown empty insect skins (Photo 1). The woods are suddenly populated with numerous large, black-bodied, red-eyed insects (Photo 2) and the air is filled from morning to dusk with loud, incessant song. The event is the mass emergence of adults of Brood XIX of 13-year periodical cicadas, or locusts as they are more commonly known in Alabama. The most recent of these events in Alabama occurred in the spring of 1985; the next will occur in the spring of 1998. Based on records of the past and results of studies at the Alabama Agricultural Experiment Station, emergence should take place sometime during the last 10 days of April and the first week of May.
History of the Periodicals
Periodical cicadas are native inhabitants of the eastern United States. Colonists in New England encountered them in the early 1600s and duly recorded and described the event.
|“……there was a numerous company of Flies, which were like for bigness unto Wasps or Bumble-Bees, they came out of little holes in the ground, and did eat up the green things, and made such a constant yelling noise as made all the woods ring of them, and ready to deaf the hearers;……”|
|“……there was such a swarm of a certain sort of insects in that English colony, that for the space of 200 miles they poysond 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..”|
The preceding quotations are excerpts from the earliest published accounts2 of periodical cicadas. Reference in each is to the emergence in 1634 of a population of 17-year periodicals. The brood to which the population belonged still exists and is currently recognized as Brood XIV. These interesting accounts describe the event in sufficient detail to make it possible, with todays knowledge of these insects, to recognize the “numerous company of flies” as cicadas. While descriptive, the accounts were not accurate in all details. For example, the “Flies” do not actually “eat up the green things, nor, with “a kind of taile or sting” are trees “thereby envenomed and killed.”
Early colonists had no prior knowledge of periodical cicadas, their habits, or the consequences of their presence. They were, however, familiar with the legends of locust plagues of the Old World. The sudden emergence of millions of noisy unknown “flyes” from “innumerable little holes in the ground” apparently appeared to be a similar plague, thus the origin of the name “locusts”3 commonly applied to cicadas.
Periodicals are divided into two groups, 17- and 13- year cicadas. These are based on the lengths of developmental periods which terminate, in spectacular fashion, with the sudden appearance of adults after an absence of 13 or 17 years. For over 200 years following discovery by colonists in New England, only the 17-year group was known. The presence of 13-year cicadas was not discovered until the mid-1800s. The 17-year cicadas are mostly northern, and the 13- year primarily southern; however ranges of the two groups overlap. That 13 or 17 years are required to complete the life cycle does not mean that adults are present only at 13- or 17-year intervals. Several broods exist within each group. The length of the life cycle for each is appropriately consistent. However, time periods of development and year of adult emergence vary among broods.
Individual periodical cicada broods are identified by number. In 1893, a standardized system utilizing Roman numerals was adopted. The 17-year broods were assigned numbers I-XVII; the 13-year broods, XVIII-XXX. Thus, the 17-year and 13-year cicadas emerging in 1893 were designated Brood I and Brood XVIII, respectively. Thereafter, numbering continued in sequence by year. Theoretically, there could be 30 broods of periodicals, but not all that have been numbered actually exist. The existence of some has never been validated, and some have become extinct. Today, 15 broods are generally recognized; three 13-year broods (XIX, XXII, and XXIII), and twelve 17-year broods (I-X, XIII, and XIV).
Originally and for many years only one species, Magicicada septendecim, was officially recognized. In the mid-1900s workers4 reported the existence of three distinct species of 17-year cicadas, M. septendecim, M. cassini, and M. septendecula. These three forms occur also in the 13-year group. There appears to be no consistent morphological difference between 17- and 13-year specimens of the same species. However, species of the 13-year cicadas have been designatedtredecim, tredecassini, and tredecula, corresponding to 17-year septendecim, cassini, and septendecula.
Periodical cicada adults (Photo 2) are spectacular in appearance and, to the casual observer, the three species look basically alike. The body is mostly black on top. The head is broad, and the abdomen tapers to the rear. Eyes are conspicuously red; legs and wing veins are reddish orange; wings are nearly transparent with an orange tint. However, color of the ventral surface of the abdominal segments varies by species (Photo 3): solid reddish brown or yellowish in M. septendecim/tredecim; black in M. cassini/tredecassini; and, segments black basally with a transverse reddish-yellow apical band in M. septendecula/tredecula. Adults are 1 to about 1 inches long. Size varies, however, by species: M. septendecim/tredecim, largest; M. septendecula/tredecula, smallest; and M. cassini/tredecassini, intermediate.
Sex of cicada adults is easily determined. Females possess blade-like ovipositors visible on the ventral surface of the abdomen (Photo 4). Males possess a pair of sound-producing, or “singing”, organs located laterally on the ventral surface of the first abdominal segment (Photo 5). Each organ consists of a large plate-like structure, the operculum, which covers a cavity containing a white or yellowish membrane and an oval, ribbed, drum-like structure called a timbal. Timbals are vibrated by strong muscles to produce the cicada song.
Periodical Broods Occurring in Alabama
Periodical cicada populations in Alabama are primarily 13-year Brood XIX. This is a southeastern brood that ranges west into Louisiana and north into Illinois and southern Iowa. In Alabama, the brood is widely distributed throughout much of the northern three-fourths of the state (see map). Ranges of three other extant broods, one 13-year and two 17-year, extend into states bordering Alabama. Brood XXIII (13-year) occurs throughout Mississippi and western Tennessee. A population believed to be of this brood was recorded in some past years at Tuscaloosa in Tuscaloosa County. Thus, small isolated populations of the brood may possibly occur in some western areas of the state. Years of last and next emergence of adults for Brood XXIII are 1989 and 2002. Ranges of eastern Broods X and XIV (17-year) extend into areas of eastern Tennessee and northern Georgia adjacent to Alabama. Some past reports have indicated the possible presence of one or both of these broods in Northeast Alabama. However, in more recent distributional maps ranges of these do not extend into the state. The last and next emergence dates for these are: Brood X, 1987 and 2004; Brood XIV, 1991 and 2008 (Brood XIV is the same brood originally discovered by colonists in the 1600s).
All three species of periodical cicadas are represented in Brood XIX. In Alabama, adults of 13-year forms designated as tredecim and tredecassini are the most common, and tredecula is the least common.
Life Cycle and Habits of Brood XIX
Habits and life cycles of all broods of periodical cicadas are much the same, varying primarily only in length of cycle (13 vs. 17 years) and year of adult emergence. Cicadas develop through three stages; egg, nymph, and adult. The nymph is the growing stage. Nymphs possess sucking-type beaks with which they feed on sap of roots of trees and other plants. Thus, nymphs develop in the soil quietly and unseen. It is the sudden, as if by signal, emergence of noisy adults that attracts attention. At the Alabama Agricultural Experiment Station, observations on the habits of Brood XIX began during the adult activity period in 1972, and were conducted in more detail during the 1985 emergence period. The studies were made in a population occurring along the Chattahoochee River in the vicinity of Goat Rock Dam in eastern Lee County. On discovery of emergence of adults in 1985, the area was visited daily or every other day initially, and at 3-day to weekly intervals thereafter for as long as activity continued. Habits and sequence of happenings, events, and development were noted and recorded throughout the period. The following presents the findings from these studies and portrays the general developmental cycle of Brood XIX as it occurs in Alabama.
As noted, cicada nymphs develop for 13 years in the soil. In spring, fully grown nymphs emerge at night leaving numerous exit holes (Photo 6). Nymphs climb onto trees and other plants or objects nearby, shed the last nymphal skin (see Photo 1), and transform to winged adults. Adults possess sucking-type beaks but feed little, if at all, and cause no discernible damage to plants by feeding. In 1985, nymphal development at Goat Rock was complete in late April. According to local residents, newly emerged adults were seen and heard singing beginning about April 29 – May 1. Inspection of the area on May 9 revealed an abundance of cast skins and numerous adults on foliage and twigs of trees and understory plants. No mating or oviposition was noted on May 9, but singing was loud and continuous. Cicada song is produced only by males, and is involved in attraction of females. Singing begins in early morning and subsides in the evening. Each species produces its own characteristic song. “Trained ears” familiar with cicada songs can identify each species by its song.
Mating was first observed on May 10; oviposition began shortly thereafter and was occurring actively by May 13. Females lay eggs in small twigs and stems of a wide variety of broadleaf trees and shrubs. Common trees utilized in the Goat Rock area were oaks, hickories, dogwood, black cherry, blackgum, sweetgum, mulberry, and elm. Diameter of most twigs and stems utilized was to inch. In the process of oviposition, the female cuts slits in twigs with her ovipositor (Photo 7). Inside each slit she constructs two grooves (Photo 8) and deposits a row of eggs in each (Photo 9). Eggs are white, spindle shaped, and approximately 2 mm long (a little less than 1/10 inch). In 225 egg grooves examined, the number of eggs per groove varied from 4 to 19, but most grooves contained 12 to 16; the mean number per groove was 13.7. The mean number of eggs per oviposition site, grooves combined, was about 27.
By May 16, adult activity had begun to decline: mating and egg-laying activity was noticeably reduced; some dead adults, primarily males, were present beneath trees (Photo 10); singing, however, was still clearly audible and constant. By May 20, singing was noticeably diminished, and ovipositing females were scarce. By May 28, singing was faint and intermittent, and adults were seldom seen. By June 3, all adult activity had ceased, and dead and dying twigs and stems of young hardwood trees and shrubs were common (See Damage Section).
Following cessation of adult activity, twigs containing eggs were collected and eggs were examined periodically for development. By June 18, embryos within eggs had developed to the point that eyespots were visible (Photo 11); by the end of June, about 6 weeks after onset of oviposition, eggs began to hatch and nymphs (Photo 12) began to emerge from twigs. Nymphs dropped to the soil and entered to begin the 13-year phase of nymphal development.
Happenings as they occurred during the study of the cicada population at Goat Rock represent the typical developmental cycle of periodical cicadas (Brood XIX) in Alabama. Date of emergence of nymphs and appearance of adults may vary a little by year and location within the state, but should occur during the period late April-early May. Adults sing, mate, and lay eggs over a period of about four weeks, usually through most of May, then die. After the 1998 event, adults of Brood XIX will not appear again until spring of 2011. Emergence of Brood XXIII is due in eastern Mississippi and western Tennessee in 2002. It is possible that some adults of this brood may appear in some areas of northwestern Alabama during May of that year.
Damage to twigs and stems of trees and shrubs is caused by ovipositing females. In the egg-laying process, females puncture bark and wood of stems in construction of pockets for eggs. Extensive ovipositional activity severely injures twigs and stems and they break or die (Photo 13). On large full-canopied trees, damage to twigs is unsightly, but does not seriously injure the tree. However, among small young trees, damage, especially to main stems, may result in loss of growth, misshapened trees, or even tree mortality. If damage occurs in orchards, such as apple, peach, or pecan, crop yields may be reduced.
Nymphs feed on root systems. In natural mixed woodlands, damage is of no consequence. In production orchards, however, vitality of trees may be reduced.
There are two general groups of cicadas in Alabama, the aforementioned periodicals and the common “annuals.” Habits and mode of development are much the same for the two groups, except for the duration of development cycles. The “annuals” consist of several species commonly referred to as harvest flies, July flies, or dog-day cicadas. Two to five years, depending on the species, are required to complete the life cycle. However, broods overlap, consequently adults are present every year.
The species of annual cicadas with which most are familiar belong to the genus Tibicen. These are large cicadas; adults (Photo 14) of some species are about 2 inches long. Typically, the body is black with areas of green above and sometimes dusted with white beneath. Eyes are black and legs greenish. Wings are clear, but are sometimes tinged at the bases with green.
Nymphs (Photo 15), like those of periodicals, develop in the soil. They emerge in mid-summer, shed the familiar skin (Photo 15), and become adults. Adults are active in July and August (dog days). Tibicen males, like those of Magicicada, possess sound-producing organs and are responsible for the familiar song commonly heard during the long hot days of late summer.
Calling Song: Attracts both males and females to the chorus. Males alternate bouts of calling (usually 1-3 calls) with short flights. The calls are 2-3 seconds long, and they are separated by silent gaps about one second long.
Court I Call: This song is constructed of a series of phrases very similar to those used in calling, but without intervening bouts of flying or walking, and often with the gaps shortened. Males produce court I, court II, and court III calls when courting a nearby female.
Court II Call: The phrases of this call are similar to those in court I songs. However, there are no gaps between call phrases, and the phrases may be shortened, with greater emphasis on the terminal downslur. Males often produce this sound shortly before attempting to mount a female.
Court III Call: this call consists of a continuous series of short, staccato buzzes, about 4-6 per second. Males produce this song while attempting to mount the female, stopping the sound only after engaging their genitalia.
Alexander, R.D. and T.E. Moore. 1962. The Evolutionary Relationships of 17-Year and 13-Year Cicadas, and Three New Species (Homoptera, Cicadidae,Magicicada). Univ. of Michigan Museum of Zoology Misc. Publ. No. 121. 59 pp.
Marlatt, C.L. 1902. A New Nomenclature for the Broods of the Periodical Cicada. USDA, Div. Of Entomol., Circ. No. 45. 8 pp.
Marlatt, C.L. 1906. The Periodical Cicada in 1906. USDA, Bur. Of Entomol., Circ. No. 14. 5 pp.
Simon, C. 1988. Evolution of 13- and 17-Year Periodical Cicadas (Homoptera: Cicadidae; Magicicada). Bull. Entomol. Soc. Of Amer. 34(4). 163-176.
USDA. 1966. Periodical Cicadas, 17-Year Locusts. Leafl. No. 540. 8 pp.
1Magicicada spp., Order Homoptera; Family Cicadidae.
2The first quotation is from Marlatt, 1906, Circ. No. 74 (see References). According to Marlatt, the account was originally reported in “New England�s Memoriall” by Nathaniel Moreton in 1669. The second account is from Simon, 1988 (see References). Simon lists the source as: Oldenburg, H. 1666. Philos. Trans. London 1:137.
3By entomological classification, the name “locust” properly belongs to a group of grasshoppers (Order Orthoptera). Nevertheless, the term, originally supplied by early settlers, is still commonly applied to cicadas today.
4Alexander and Moore (see References).