Wednesday, June 11, 2008

Cicada Songs

"They sound like a thousand cars with bad power steering, all turning in tight little circles." At least, that's what one of my humans said to the other. They were talking about cicadas--periodical cicadas--and they have emerged on Cape Cod. In our town, there are not a lot of them. However, in the next town over, the sound can be deafening. Cicadas made the front page of today's Cape Cod Times. They were discribed as "what sounds like a chorus of police and fire sirens headed to a massive accident." --

(To see the front page of the Cape Cod Times, go to:
A couple of days ago, I witnessed a curious phenomenon: my human partner was outdoors with this small, odd-looking box that occasionally made clicking noises. She was staring at one of those cicada bugs that there has been so much fuss about. Then she found something on a tree to stare at. Afterwards, she started working on the computer and a bunch of different cicada pictures came up on the computer screen. I thought they were rather interesting, so here they are.


"....No other insects in North America excite as much curiosity and wonder as do periodical cicadas when they make their sudden appearance every 13 or 17 years. These cicadas are widely distributed in the United States east of the Rocky Mountains, but occur nowhere else on earth. There are seven species of periodical cicadas—four with 13-year life cycles and three with 17-year life cycles, distributed over several broods (see map below). The best way to identify individual species is by sound because each cicada song is species specific. After years of living in underground tunnels, thousands of periodical cicadas emerge from the earth, as if by a predetermined signal, shed their nymphal skins, and spread out through the nearby trees and bushes. Up to 40,000 can emerge from a under a single tree!

The cicada's precise but prolonged time schedule revolves around survival for the masses. When a large population of juicy insects appears on the scene, predators make the most of the situation, but simply cannot eat all the insects. Thus, a significant number of cicadas live to reproduce. Long-lived predators may actually remember the feast and return to the scene in subsequent years. Short-lived predators, being well fed from the cicada banquet, reproduce successfully and often leave a larger population to await next year’s emergence. However, "next year" doesn’t happen for at least 13 years, so the periodical cicada is able to outlast and escape most of its enemies.

From morning till night the males fill the air with their loud, droning song. The song is like the familiar sound of the common dog-day cicada so typical of summer evenings, only it is louder and heard at the end of spring. The males are the only ones singing...." [From: "A Trill of a Lifetime"(originally published in The Illinois Steward, Summer 2004)text by Susan L. Post. For complete text, go to:]


"What is a periodical cicada?

Cicadas are flying, plant-sucking insects of the Order Hemiptera; their closest relatives are leafhoppers, treehoppers, and fulgoroids. Adult cicadas tend to be large (most are 25-50mm), with prominent wide-set eyes, short antennae, and clear wings held roof-like over the abdomen. Cicadas are probably best known for their conspicuous acoustic signals or "songs", which the males make using special structures called tymbals, found on the abdomen. There may be as many as 3000 different cicada species worldwide.

All but a few cicada species have multiple-year life cycles, most commonly 2-8 years (de Boer and Duffels 1996). In most cicada species, adults can be found every year because the population is not developmentally synchronized; these are often called "annual" cicada species. In contrast, populations of the periodical cicada species are synchronized, so that almost all of them mature into adults in the same year. The fact that periodical cicadas remain locked together in time is made even more amazing by their extremely long life-cycles of 13 or 17 years.

Periodical cicadas are found in eastern North America and belong to the genus Magicicada. There are seven species -- four with 13-year life cycles (including one new species described in 2000), and three with 17-year cycles. The three 17-year species are generally northern in distribution, while the 13-year species are generally southern and midwestern. Magicicada are so well-synchronized developmentally that they are nearly absent as adults in the 12 or 16 years between emergences. When they do emerge after their long juvenile periods, they do so in huge numbers, forming much denser aggregations than those usually achieved by cicadas. Many people know periodical cicadas by the name "17-year locusts" or "13-year locusts", but they are not true locusts, which are a type of grasshopper.

Magicicada adults have black bodies and striking red eyes and orange wing veins, with a black "W" near the tips of the forewings. Most emerge in May and June. Some of the annual cicada species are sometimes mistaken for the periodical cicadas, especially those in the genera Diceroprocta and Okanagana; these other species emerge somewhat later in the year but may overlap with Magicicada. The Okanagana species are the most potentially confusing because of their similar black-and-orange coloration. The best way to identify cicada species is by the sounds that they make, because cicada songs are nearly always species-specific. ----------------

Magicicada life cycles

Cicada juveniles are called "nymphs" and live underground, sucking root fluids for food. Periodical cicadas spend five juvenile stages in their underground burrows, with each stage ending with eclosion (shedding of the old nymphal skin). Their burrows are found anywhere from several inches to a few feet underground, depending on nymphal age and the nature of the soil.

In the spring of their 13th or 17th year, a few weeks before emerging, the nymphs construct exit tunnels to the surface. These exits are visible as approximately 1/2 inch diameter holes, or as chimney-like mud "turrets" the nymphs sometimes construct over their holes. On the night of emergence, nymphs leave their burrows around sunset, locate a suitable spot on nearby vegetation, and complete their final molt to adulthood. Shortly after ecdysis (molting) the new adults appear mostly white, but they darken quickly as the exoskeleton hardens. Sometimes a large proportion of the population emerges in one night. Newly-emerged cicadas work their way up into the trees and spend roughly four to six days as "teneral" adults before they harden completely (possibly longer in cool weather); they do not begin adult behavior until this period of maturation is complete.

It appears that the particular night of emergence may be determined by the soil temperature; nymphs emerge when the soil temperature inside the exit tunnel (and therefore the body temperature of the nymph) exceeds approximately 64 degrees F (Heath 1968). Because emergence is temperature- dependent, periodical cicadas tend to emerge earlier in southern and lower-elevation locations. For example, periodical cicadas in South Carolina often begin to emerge in late April, while those in southern Michigan do not appear until June. The best way to predict the time of emergence for your area is to check records from the prior emergence in that location, by asking longtime residents or by searching local newspaper archives. The date of emergence does not vary much between generations, although unusual springtime weather conditions may accelerate or delay the emergence by a week or so.

After their short teneral period, males begin producing species-specific calling songs and form aggregations (choruses) that are sexually attractive to females. Males in these choruses alternate bouts of singing with short flights until they locate receptive females (see the Magicicada behavior section below). Contrary to popular belief, adults do feed -- by sucking plant fluids; adult cicadas will die within days if not provided with living woody vegetation on which to feed. Magicicada feed from a wide variety of deciduous plants and shrubs, but usually not from grasses.... Mated females excavate aseries of Y-shaped eggnests in living twigs and lay up to twenty eggs in each nest (Marlatt 1923). A female may lay as many as 600 eggs (Marlatt 1923)....

Why are there so many of them?

Periodical cicadas achieve astounding population densities, as high as 1.5 million per acre (Dybas 1969). Densities of tens to hundreds of thousands per acre are more common, but even this is far beyond the natural abundance of most other cicada species. Apparently because of their long life cycles and synchronous emergences, periodical cicadas escape natural population control by predators, even though everything from birds to spiders to snakes to dogs eat them opportunistically when they do appear. Magicicada population densities are so high that predators apparently eat their fill without significantly reducing the population (a phenomenon called "predator satiation"), and the predator populations cannot build up in response because the cicadas are available as food above ground only once every 13 or 17 years. Periodical cicadas do have a specialized fungal parasite (see the Magicicada diseases and deformities section), but its effects on Magicicada population density are not well understood. Individual periodical cicadas are slower, less flighty, and easier to capture than other cicadas, probably because the safety afforded by their great numbers means that the risks of predation for an individual are low. Explaining the evolution of such an unusual life strategy is one of the most difficult problems for periodical cicada biologists.

This year (2008), the large Appalachian 17-year Brood XIV will appear. As is true for most of the 17-year broods, all three 17-year species will be present in many locations. A web-based effort to map the distribution of this brood in more detail is underway.... Sometimes periodical cicadas emerge "off-schedule" by one or more years. This phenomenon is called "straggling," although straggling cicadas can emerge either later or earlier than expected. The most common form of straggling is one-year premature or delayed emergences, usually involving small numbers of cicadas. Unexpectedly, the next most common form of off-schedule emergence is four-year premature appearances by 17-year cicadas, and these events sometimes involve many thousands at once. In 2000, many cicadas emerged four-years early across the range of Brood X. A similar event was observed in 1969 in the Chicago area, four years before the normal emergence in 1973 (Dybas 1969). These events help us to understand the origin of the various same-cycle broods as well as the developmental mechanisms underlying Magicicada speciation, which tends to involve permanent shifts between life cycle types (see details on the seven species and their relationships below). Straggling makes it difficult to construct accurate maps of periodical cicada brood distributions (Marshall 2001), partly because historical reports of off-schedule emergences often contain little or no information about how many cicadas were seen.

Magicicada behavior

As in nearly all cicada species, male periodical cicadas produce "songs" using a pair of tymbals, or ridged membranes, found on the first abdominal segment. The abdomen of a male cicada is hollow and may act as a resonating chamber; the songs of individuals are loud, and large choruses can be virtually deafening. Females of most cicada species do not have sound-producing organs. Both sexes hear the sounds of the males as well as other sounds using membranous hearing organs called "tympana" found on the underside of the abdomen.
Over the course of an emergence, males congregate in "choruses" or singing aggregations, usually in high, sunlit branches. Females visit these aggregations and mate there, so choruses contain large numbers of both sexes.

Males of all Magicicada species (each described individually below in the Magicicada species section) produce alarm calls when handled, calling songs that attract males and females to the chorus, and one or more courtship calls when approaching and attempting to mate with females. Five different male acoustic signals have been described for the -decim and -cassini cognate species. Samples of most of these sounds are included below. These species have calling and courting signals that differ in pitch (frequency) and other characteristics, but the signals have have similar structures, so they can be described together. The functions of these signals are not entirely understood, but they have been given names to indicate their suspected function. The acoustical behaviors of the -decula species have not been as well characterized.
Female Magicicada produce timed "wing flick" signals in response to male calls, and the timing of this signal in relation to the male call is species-specific for species of the same life cycle. The signal consists of a quick flip of the wings that creates a broad-frequency sound that can vary from a soft rustle to a sharp snap. Males are able perceive both the visual and acoustic components of the wing-flick.

A chorusing male perceiving a female signal increases his number of calls relative to movement distance, increasing the odds that he will elicit further responses from any nearby female. If the male receives multiple responses, he ceases sing-fly behavior, begins CI courtship, and engages in a signaling duet with the wing flicking female, evidently for the purpose of locating her. Between calls, duetting males often walk towards the signaling female, and while approaching, begin CII calling. After contacting the female or while preparing to mount, the male begins CIII calling, which he continues until he mounts and copulates. Under some circumstances, males engaged in duets acoustically obscure the downslurs of potential competitors, reducing the likelihood of a female response and increasing the likelihood that competing males will continue chorusing, depart and search elsewhere. Although female wing-flick signaling is known in some Australian and New Zealand cicadas (e.g., Lane 1995), this is the first reported incidence of female signaling in North American cicadas.... "
[For complete text, go to:]

For pictures of the May 29th, 2008 Cicada Brood:

If you now have "Cicada Mania," go to:

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