Life Cycle Of Cicadas
Cicadas have prolonged nymphal stages, which are spent within the ground, sucking juices from the roots of plants, especially woody species. Most cicada species have overlapping generations, so that each year some of the population of subterranean nymphs emerges from the ground and transforms into a fairly uniform abundance of adults, as is the case of the dog-day or annual cicada (Tibicen pruinosa).
Other species of cicadas have non-overlapping generations, so there are periodic events of the great abundance of adults and their noisy summer renditions, interspersed with much longer periods during which the adult animals are not found in the region. The irruptive adult phase occurs at intervals as long as 17 years, in the case of northern populations of the periodical cicada (Magicicada septendecum), which has the longest generation time of any plant-sucking insect. Southern populations of the periodical cicada gave generation times as short as 13 years, and are usually treated as a different species.
The periodical cicada spends most of its life in the ground, in its developmental nymph stages. During years of irruption or peak emergence, the ground in late spring and early summer can be abundantly pock-marked with the emergence holes of the mature nymphs of this species, at a density greater than one thousand per square meter. The stout-bodied nymphs emerge from the ground and then climb up upon some elevated object, where they metamorphose into the adult form, which lives for about one month. During years when periodical cicadas are abundant, the strange-looking, cast exoskeletons of their mature nymphs can be found in all manner of places.
The adult periodic cicada is black or dark brown, with large, membranous wings folded over its back, and large, red eyes. The females have a strong, chisel-like ovipositor, which is used to make incisions in small branches and twigs, into which her eggs are deposited. The incisions severely injure the affected twigs, which generally die from the point of the incision to the tip. Soon after hatching, the small nymphs drop to the ground and burrow in, ready for a relatively long life of 17 years. The subterranean nymph excavates a chamber beside the root of a woody plant, into which the cicada inserts its beak and feeds on sap.