Cicadas

Cicadas

Biology of cicadas

Life cycle of cicadas

Cicadas and people

Cicadas are insects in the order Homoptera, family Cicadidae. Male cicadas make a well-known loud, strident, buzzing sound during the summer, so these unusual insects are often heard, but not necessarily seen. Cicada species are found in closed and open forests of the temperate and tropical zones.

Biology of cicadas

Cicadas are large dark-bodied insects, with a body length of 2 inches (5 cm), with membranous wings folded tentlike over the back and large eyes.

Male cicadas have a pair of small drumlike organs (tymbals), located at the base of their abdomen. These structures have an elastic, supporting ring, with a membrane extending across it (the tymbal membrane). The cicadas’ familiar very loud buzzing noises are made by using powerful muscles to move the tymbal rapidly back and forth, as quickly as several hundred

times per second. The actual sound is made in a manner similar to that by which a clicking noise is made by popping the center of the lid of a metal can back and forth. The loudness of the cicadas’ song is amplified using resonance chambers, known as opercula. Each species of cicada makes a characteristic sound.

Cicadas are herbivorous insects, feeding on the sap of the roots of various types of perennial plants, most commonly woody species. Cicadas feed by inserting their specialized mouth parts, in the form of a hollow tube, into a plant root, and then sucking the sap.

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 and transforms into a fairly uniform abundance of adults, as is the case of the dog-day or annual cicada (Tibicen pruinosa ).

Other species have nonoverlapping generations, so periodically there is a great abundance of adults and their noisy summer renditions, interspersed with much longer periods during which the adults 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 have generation times as short as 13 years, and are usually treated as a different species.

KEY TERMS

Irruption— A periodic, sporadic, or rare occurrence of a great abundance of a species. The periodic cicada, for example, is irruptive on a 17-year cycle.

The periodical cicada spends most of its life in the ground, in its developmental nymph stages. During years of irruption or peak emergence—late spring and early summer—the ground can be pockmarked with the emergence holes of the mature nymphs of this species, at a density greater than 100 per square foot (1, 000/m²) 1, 000 per square meter (100 per sq ft). The stout-bodied nymphs emerge from the ground and then climb up upon some elevated object, where they meta-morphose into the adult form, which lives for about a 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.

Cicadas and people

When they are breeding in abundance, some species of cicadas cause economic damage by the injuries that result when the females lay their eggs in the branches and twigs of commercially important species of trees. The periodical cicada is the most important species in this respect in North America. This species can cause a great deal of damage in hardwood-dominated forests in parts of eastern North America. The damage is not very serious in mature forests, but can be destructive in younger forests and nurseries.

Although cicadas are not often seen, their loud buzzing noises are a familiar noise on hot sunny days in many regions. As such, they are appreciated as an enjoyable aspect of the outdoors.

Bill O. Freedman