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Cicadas

The cicadas (sih-kay-duh) comprise a family in the insect order Homoptera, a very diverse group that also contains the leafhoppers, treehoppers, spittlebugs, aphids, and scale insects. There are more than 2,000 species of cicadas worldwide most of which occur in the Tropics. About seventy-five species occur in North America, only four in Massachusetts.

One species (Magicicada septemdecim) is the periodical cicada that emerges once every seventeen years; the other is the annual or dogday cicada (Tibicen linnei) which emerges every one or two years.

IDENTIFICATION
Probably because of their regular population explosions, periodical cicadas have been confused with certain large grasshoppers that occur in crop-devastating swarms. It is these and other grasshoppers, not cicadas, that are properly called "locusts." Another common name for cicadas is "harvester flies" because their "song" is characteristic of late summer days.

The smaller (1 to 1.5 inch) periodical cicada is distinguishable by its black body, its more slender form, red eyes and reddish-orange tinge on the wings. The body of the dogday cicada is approximately 2.25 inches long, medium brown, with greenish wing venation.

LIFE CYCLE
Female cicadas make forty to fifty slits in the twigs of broad-leafed trees, as well as weed and grass stems, in which to insert up to 400 eggs. The first stage nymph, which resembles a large, pale ant with front legs enlarged and modified for digging, hatches in six to seven weeks, drops to the ground, and buries itself two inches to two feet into the earth. This nymph lives by sucking juices from roots and grows gradually through eight stages before maturity. The periodical cicada lives more than half of its seventeen-year lifespan as a mature nymph underground, and it is believed that dogday cicadas spend at least four years underground.

When the magic year arrives, the nymph digs to the surface, normally during the night, crawls up a tree trunk, and anchors itself with its claws. The skin of the back then splits, and the winged adult emerges and seeks its preferred habitat. The dogday cicadas that we hear each summer are solitary insects; we seldom see them. Periodical cicadas, by contrast, often cover lower vegetation and any other surface in swarms immediately after they hatch, and can't be missed where they occur. Like most Homopterans, adult cicadas have tube-like mouthparts adapted for sucking plant juices, and may occasionally feed from tree branches. However, they may not feed at all during their five-to-six week adulthood.

CICADA BROODS
Though some species are called annual cicadas because they are present every year, all species take at least four years to mature in the ground. Among periodical cicadas, there are numerous different "broods," some of which are on thirteen-year cycles (southern) and some on seventeen-year cycles (northern). Each brood has its own unique range, population size, and emergence cycle; there are twenty to thirty different broods in North America, five of which occur in New England. (Each of these broods has been identified by scientists and designated with a Roman numeral.) Brood XIV is the one Governor Bradford recorded in 1624 and may be the most spectacular one to occur in Massachusetts. This brood extends from Plymouth and Bristol counties south to Georgia and west to Illinois. Writing of the 1923 emergence for the Bulletin of the Boston Society of Natural History, veterinarian Langdon Frothingham noted on June 25 that, "The air is full of them, often landing on you and singing in your ear."

HOW CICADAS 'SING'
The slightly plaintive drone of the dogday cicada probably evokes the dogdays of late summer more powerfully than any other natural sound. This astonishingly loud sound issues from a pair of organs called "tympana" located at the base of the males' abdomen. The tympana is a complex mechanism that consists of a series of three membranes inside a resonating chamber. One of these membranes (the tymbal) is flexed by a powerful muscle somewhat in the way a metal can top can be pushed in and released to create a loud click. Done in rapid succession and amplified by the resonating chamber, the familiar whine is produced. Different species of cicadas can be identified by the distinctive tone of their hum.

ARE CICADAS HARMFUL?
Cicadas are among the most benign of insects. They can buzz impressively when trapped, but they don't sting or bite, or carry any disease communicable to people. Nor do they poison fruit or foretell hard times as superstitions tell.

Neither the root-sucking nymphs nor the adults do any significant damage to trees or other plants. Because of their great abundance, when female periodical cicadas lay eggs in fruit and ornamental trees they can sometimes cause the tips of branches to break. It has been suggested that shade and forest trees may actually benefit from cicada "damage," which acts in effect as a natural pruning mechanism. Small trees can be protected by covering them with netting or any other open-weave material during the adults' life span (five to six weeks).

Cicadas have many natural enemies including birds, mites, fungal disease, and a splendid, big, black and yellow parasitic wasp called a cicada killer that catches and paralyzes its prey, then drags the victim into a subterranean burrow and uses it for an egg repository and as food for the larva.

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