The gentle drizzle has let up and the dappled light paints the forest in browns and greys. As the light dances between the tree trunks, it is accompanied by a steady murmur. The musicians of the forest are out, their melody pulsating through the air, almost as if in sync with the dancing rays. From my room in a forest lodge in Kodagu, I listen to the lively medley of cicadas announcing the arrival of the monsoon. While the song of the cicada (Cicadoidea) is probably familiar to all of us, the lives of these tiny insects, heard more often than seen, remain shrouded in mystery.
With their large eyes and translucent wings, these creatures have a fascinating lifecycle. The powerful song of the cicada is the male’s calling card, and the female arrives in response. Post mating, she lays her eggs on twigs or grass stems. The emerging young ones look like termites, and stay on the plant, feeding on sap till they are ready to drop down to the ground. This marks the beginning of the next stage of their lifecycle, where they burrow into the earth, living and feeding on roots. Tunnelling through the earth with their powerful front legs, the nymphs burrow and build chambers underground, living a major part of their lives underground, till they are finally ready to emerge as adults.
The time the nymph spends underground varies from species to species. Of India’s approximately 200 recorded species of cicadas, most spend at least a couple of years in the nymphal stage. Once a year, they emerge just before the arrival of the monsoons. When the conditions are just right, under cover of darkness, the nymphs crawl out and shed their nymphal skin, transforming into adult cicadas with pale, luminous wings. Soon after, the forest is thrumming with the rhythm of cicadas announcing, in style, that the rainy season is on its way. A lucky and observant walker might find cast-off nymphal skins on tree trunks.
While cicadas emerge annually in most parts India, there is a one periodic cicada, the Chremistica ribhoi in Meghalaya that emerges only once in four years. Others spend an even longer portion of their life under the earth. In some parts of the world, periodic cicadas spend up to 17 years as nymphs underground.
Historically, across cultures, cicadas have been symbolically linked to ideas of rebirth and transformation in both folklore and art. In China during the Han Dynasty, jade cicadas were placed on the tongue as part of the burial ceremony to ensure that the departed have voices in their afterlife. The native American Onondaga believe that cicadas emerge from the earth, bringing with them an opportunity to renew their relationship with nature and their ancestors. The ancient Greeks were not only captivated by the emergence of cicadas and their distinctive tune, they also believed cicadas survived only on dew and air. Evocative as that is, we now know that adult cicadas feed solely on plant sap.
The song of the cicada, that powerful hum from such a slight insect, has also captured the imagination of people down the ages. In the last century, novelist John Berger, in his Booker Prize winning novel G., poignantly asks “Do you know the legend about cicadas?” and then elaborates, “They say they are the souls of poets who cannot keep quiet because, when they were alive, they never wrote the poems they wanted to.”
In most species, the male cicada produces this remarkable sound with the help of a combination of unique adaptations. For one, the body is like a hollow musical instrument; akin to a violin or guitar with air-filled pockets that behave like echo chambers, amplifying the sound the creature generates. The sound itself is produced by specialised tymbals, thin membranous structures with thick ribs, located on either side of the abdomen. A muscle pulls these ribs inward and then releases them, the movement making a sharp sound. Rapid repetition of this action at an astonishing speed of 300 to 400 times per second generates the distinctive tambourine-like music the cicada produces. Varying body sizes produce different sound frequencies — bigger-bodied cicadas create deeper calls than smaller-bodied cicadas. In answer to the male’s song, the female cicada replies with a soft click that sounds like a switch flicked. Once the female arrives in response to his song, the male switches to a courtship anthem.
In some species, males also create distinct chorus songs, as well as alarm and distress calls when startled. Unlike their cousins the crickets that sing at night, the “chrrrs” of most cicadas are usually heard during the day or at dusk, depending on the species and weather. Cicadas are also often confused with locusts, other grasshoppers, and katydids (all Orthopterans) but the easiest way to tell them apart is that Orthopterans have large hind legs.
As the forest reverberates with the sound of cicadas, I wonder how the tiny conductors of this booming orchestral concert withstand their own volume, particularly as they are in the eye of the storm. (Cicadas are the loudest insects in the world, the intensity of their sound as high as 120 decibels. Compare that to an average hair dryer or vacuum cleaner that runs at 70-90 decibels.) The answer lies in a nifty little trick that male cicadas use — they fold their tympana, the insect equivalent of ears, thus limiting what they hear.
Much of what goes on in the lives of cicadas remains a mystery. The diversity of cicadas in India is significant, and an increased spurt in research in recent years has uncovered new species in the Western Ghats and Meghalaya. On another rainy day in 2014, similar to the one I was enjoying in Kodagu, a new species of cicada, the tiny Rustia minuta, was discovered in South Goa. As I listen to the various sounds typical of the Indian monsoon, I wonder what other discoveries lie in store.