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In northern Illinois and surrounding areas, three species of Magicicada emerge from the soil every 17 years for a brief above-ground visit. Brood XIII will emerge when soil temperature reaches approximately 65° F. Spectrum data loggers are busy tracking soil temperature near Spectrum headquarters in northern Illinois to estimate when to expect their arrival.  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. 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 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. The picture below shows Magicicada septendecula feeding, with the piercing-and-sucking mouthparts visible just behind the forelegs. 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). Below is a photograph of Magicicada eggnests. The adult emergence lasts for about four to six weeks after the appearance of the first nymphs. Six to ten weeks or so after oviposition, in midsummer, the eggs hatch and the new first-instar nymphs drop from the trees, burrow underground, locate a suitable rootlet for feeding, and begin their long 13- or 17-year development. Source: The University of Michigan Museum of Zoology - Insect Division http://insects.ummz.lsa.umich.edu/fauna/michigan_cicadas/Periodical/Index.html Other links http://www.suburbanchicagonews.com |
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