Greek summer: heat, wind, and draught – and the endless songs of the crickets and the cicadas. Of the cicadas in particular. The screech of Cicada orni tirelessly shrills in the trees all summer long from dawn to dusk. Yes, crickets may chirp, but cicadas shrill. It’s hard to believe what an intense sound this little creature is able to produce.
And their vocalizations are not the only amazing thing about the cicadas. These insects are fascinating. We know about 40,000 cicada species. They live wherever plants grow, and play an important role in the ecosystem and the food chain. Many cicadas are specific to a host plant and are adapted to special environmental conditions so that they are very sensitive to any interference with their natural environment. About half the cicada species occurring in Germany are listed on the Red List of Endangered Species. Cicadas are altogether harmless insects: they cannot bite or sting. In many parts of the world cicadas are actually eaten by humans; worldwide there are more than 70 edible cicada species.
Anatomy and Locomotion
Cicadas are easily recognizable by their typical anatomy. They have a rather sturdy body and hold their wings at an angle above their body. The head is short and broad with short antennae and eyes set wide apart at the sides of the head. Cicadas can see well through large compound eyes which enable them to localize pursuers and also to perceive colors. On the forehead they have, like most insects, three small ocelli (single eyes), which are believed to serve primarily for horizon detection, light-compass orientation, and light intensity measurement.
Many species of cicadas occur on Naxos, but the most conspicious is the very abundant Cicada orni. This species is brownish in colour. The wings are transparent with several dark spots along the veins. The end of the abdomen has a white ring. Cicada orni reaches a size of almost 3 cm in length. It usually sits in large trees (e.g., olive and plane trees), mostly on the underside of thick branches, but due to the camouflage it is hard to detect.
Cicada orni in an olive tree. Note the small antennae and the way the animal holds its wings at an angle.
Here you can see the large eyes and the white abdomen tip.
A cicada head from above with the short, thin antennae, the compound eyes at the sides of the head and the upper two of the three ocelli.
Cicadas are good flyers. In flight, the front wings and the smaller rear wings are coupled together by small hooks. Many cicadas (but not the singing cicadas, which include Cicada orni), can jump as well. Spittlebugs (a member of the Cicada family) are Olympic champions in jumping: although only half a centimeter in size, they can jump 70 cm high. Like grasshoppers, they jump with their hind legs, which are not, however, either large or conspicuous. They accomplish their “explosive” jumping performance by means of a special technique: they build up a tension in the legs, which is then suddenly discharged, whereby the Spittlebug is flung forward as from a catapult.
The wings of cicadas are completely transparent except for the veins and several characteristic dark spots. It seems incredible that these delicate structures can withstand the strain of flying.
Development and Food
Cicadas are insects with incomplete metamorphosis, which means that they have no pupal stage, but go through several larval stages (usually five) during which they gradually become more similar to the adult. While the adults live less than a year, it takes several years (in Cicada orni five) until the larvae have developed into adults. In North America there are cicada species that need 13 or even 17 years for their development. Astonishingly, in some species most individuals hatch in the same year in near simultaneity, just a few days apart. Thus these species appear only every 13th or 17th year for a short time in great numbers until the adults have laid their eggs and die.
Cicada larvae live underground. They feed on plants, sucking sap from their roots. Their front legs are designed as shovels, with which they dig 15 cm to 3 m deep into the ground. To hatch, they leave the ground and cling to a plant stem, where the empty larval skin remains.
On the empty skin of a hatched cicada, you can see the “shovels”, the unfinished wings, the eyes, etc. The skin cracks open at the back to allow the mature insect to hatch.
Like the larvae, the adult cicadas feed by sucking plant saps, using their long proboscis (snout) to pierce the plant and suck. When the animal is not feeding, the long proboscis is placed under the body. Many species feed only on a few specialized host plants. While many cicadas suck the sugary phloem sap, Cicada orni taps the the watery sap of the xylem, which streams from the roots upwards. Accordingly, they have to absorb much more water in order to meet their nutritional needs. Unlike many other insects, cicadas do no damage to the host plants even when they occur in great numbers.
Here you see the long, thin proboscis on the underside of the cicada, with which the animal bores a hole into the vascular bundles (water transport system) of the trees and sucks the juice. The proboscis is another surprising organ of the cicada: how can such a thin, flexible snout be strong enough to drill a hole into the bark of a tree?
The Song and its Perception
And now for the song. Only male cicadas sing. They use the song in order to mark a territory, to drive away other males, and to attract females. Unlike grasshoppers, cicadas produce their vocalizations not by stridulation of the legs and wings, but by a drum-like organ, the tymbal, which is located on both sides of the front part of the abdomen. The tymbal consists of a small membrane enforced by ribs that produces a clicking sound when it buckles inward and outward as special muscles on its inside alternately contract and release. The air-filled abdomen serves as resonator.
Here you can see, just behind the wings, the tymbal of the male cicada.
It is rather astonishing what a loud noise this little insect can produce with its tymbal: Some species reach up to 120 dB, the equivalent of a chainsaw or a jackhammer! Fascinating too is the persistence with which cicadas sing for hours all day long – or in fact all summer long. Many smaller cicada species produce similar songs as well, but they are so high-pitched that they are inaudible to human ears.
The cicadas possess the typical hearing organ of insect, the tympan, which consists of two fine membranes that perceive vibrations. The cicadas’ tympana are located on the underside of the abdomen. In other parts of their body they have simpler vibration receptors, which possibly provide information on the substrate on which they sit, by the perception of the vibrations caused by their own vocalizations that are transmitted into the underground.
The Cicadas in Myth and Art
Owing to their distinctive song and other impressive features, cicadas appear in the myths of many nations (Southern Europe, Asia, and America). Already in Mycenaean illustrations insects are pictured that are considered to be cicadas. Cicadas are mentioned in ancient Greek literature such as the Iliad. Anacreon wrote a hymn to the “godlike” cicadas, which was translated by Goethe, among others. From the poet Xenarchos comes the utterance: “Happy the cicadas, because they have mute wives”. The best-known narrative which deals with cicadas is the famous Aesop fable of the cicada (not cricket or grasshopper as it is often translated) and the ant.
In various cultures cicadas occur as symbols of the Muses and the art of Singing (Greece) and of the Troubadours (medieval Europe, especially southern France). They also symbolize rebirth (China) and immortality (North American indigenous peoples) through their metamorphosis: the shedding of their skin was interpreted as a symbol for discarding the physical needs of the body and thereby achieving the “liberation” of the soul. In ancient Athens cicadas were used as a symbol of the autonomy of the city, as the adults seem to be born from the earth.
see also: Animals