ARTHROPOD MUSEUM NOTES
Number 80 • April 7, 2011 • Jeffrey K. Barnes
Genus and species: Magicicada spp.
This spring many Arkansans and other southerners will witness one the most astounding acts of nature – the near simultaneous emergence of millions of large, noisy, black and orange periodical cicadas.
Cicadas are among the largest and loudest insects found in Arkansas. About two dozen species in six genera have been recorded as likely occurring in the state. Males produce species-specific songs, mostly during daytime, to attract females. Females slash twigs with their ovipositors and place eggs deep in the plant tissues, often killing twig ends and causing significant damage to orchards and ornamental plantings. Upon hatching, the nymphs fall to the ground and burrow down to tree roots from which they suck xylem fluids. This food is low in nutrients so the insects require long nymphal periods in order to mature. Mature nymphs dig their way to the surface and find an appropriate place for the adults to emerge. Typically, adults live only a few weeks.
Periodical cicadas are placed in the genus Magicicada. At 1.0-1.2 inches long, they are smaller than the common dog-day cicadas of the genus Tibicen, and they are readily recognized by their distinctive red eyes, orange wing veins, and yellow or orange stripes on the underside. Adults from several United States geographic areas east of the Great Plains emerge together in predictable 13-year or 17-year cycles, sometime in numbers as large as 1.5 million per acre. Each geographic group is called a brood. Broods from the northern states usually have 17-year cycles of adult emergence, whereas those from the south usually have 13-year cycles. Theoretically there are 30 broods, 17 broods of 17-year cicadas and 13 broods of 13-year cicadas. However, it appears that several broods have disappeared due to human activities such as plowing and paving. Only 15 broods remain viable. Previously, it was thought that there were 3 morphologically distinct species, differing also in coloration, size, song, mating behavior, and habitat preference. Because 17-year and 13-year cicada adults can only emerge together, and thus potentially interbreed, every 221 years, most scientists argued that there were six species, with each 17-year species having an almost exact 13-year complement. More recently, in 2000, a fourth species of 13-year cicada was described. Two of the 13-year species are very similar and can be distinguished only by their songs in areas where their ranges overlap or by their DNA.
Adults emerge in spring, beginning in late April or early May, and emergence events last only six to eight weeks. Individual adults live for only about three weeks. Male cicadas form chorus centers that attract females for mating purposes. Depending on the size of the chorus, the noise level can be deafening. Periodical cicada emergences can be regarded as environmental resource pulses. Mass emergence is regarded by some scientists as a survival trait called predator satiation. The cicadas overwhelm potential predators with their sheer numbers. Predators become satiated early in the season, thus ensuring the survival of most potential prey individuals. Tree growth declines the year before a mass emergence because of root feeding by maturing nymphs. On the other hand, predatory moles do well feeding on maturing nymphs the year before an emergence. Periodical cicadas provide food for a wide variety of predators, including birds, fish, copperhead snakes, box turtles, spiders, dragonflies, and assassin bugs.
Arkansas hosts two major broods, Brood XIX and Brood XXIII, both of the 13-year variety. The Great Southern Brood of periodical cicadas, also known as Brood XIX, consists of four species that emerge together as adults in great numbers once every 13 years in the southern United States. This brood, the largest of the 13-year variety, occurs over a 15-state area, and parts of all Southeastern states except Florida will experience this emergence. This brood was first recorded in 1803, and adults have emerged 15 times, last appearing in 1998. They are due to appear again in the spring of 2011. Although the emergence occurs over a large area, adults have a patchy distribution. In Washington County, Arkansas, cicada emergence areas are found in forest habitats within the White River drainage, presumably the main cicada dispersal route into northwestern Arkansas and now the western limit of Brood XIX. Cicadas do not emerge from former prairie habitats.
Adults of Brood XXIII, the Lower Mississippi River Valley Brood, last emerged in 2002 and will appear again in 2015, primarily in the Crowley’s Ridge area. Brood IV of the 17-year variety, known also as the Kansas Brood, occurs mostly to the north and west of the state, but a few individuals might emerge within the state. Brood XXIII also emerges in Arkansas every 13 years, and it is due to appear again in 2015
Periodical cicadas are harmless to humans. They neither bite nor sting. However, they can damage vegetation through their oviposition activities, as noted above. Adults feed on a wide variety of deciduous plants and shrubs, but this activity causes negligible damage. It is not advisable to plant trees or shrubs just before a mass emergence.