Music is the heart and soul of everything in nature. From the wonderful calls of avian and mammalian life to the rhythmic melody of leaves swaying in the breeze to the humming sound of wind finding its way through thick undergrowth; nature is filled with a lot of musical renditions.
A variety of these compositions have been used to depict typical wilderness, especially in movies, to give the viewer a visual and an aural sense of the wild. But, nothing can be a closer depiction than the resounding, resonating, constant buzzing and clicking sounds emanating from all around, echoing from trees and shrubs, with eerie silences forming interludes in the overall musical composition. The artists responsible for these wonderful renditions are amazing little creatures called Cicadas.
Cicadas are insects of the Hemiptera order, in the superfamily Cicadoidea. They live in predominantly temperate to tropical climates, in a wide range of habitats. Around 2500 species of Cicadas have been described so far. They are closely related to leafhoppers and spittlebugs.
They spend a large part of their early life underground, feeding on sap from the roots of trees and plants. Plant sap forms the primary source of nutrition for adults as well. Cicadas have mouthparts adapted for piercing and sucking on the stems of plants and succulent shoots. Sap, being largely sugar and water, Cicadas have to suck up large quantities to make a decent meal. As a result, large amounts of a weak, sugary solution are rapidly excreted. And, when many of them do it at the same time, it drops down like rain. So, if it appears to be raining in a rain forest, despite clear skies, it most definitely means Cicadas are feeding overhead.
Cicadas stay underground for different durations, depending on the species. Some may emerge out of the ground every year while others may take as long as 2 to 17 years.
As soon as they come out of their underground abode, they undergo a process of transformation, changing from their nymph stage to an adult. This process is known as moulting.
For this, they first find a small plant or a tree and settle down on it. Slowly, their old outer covering splits open and the Cicada starts emerging with its fresh, new coat.
Moulting is a slow and strenuous process consuming a lot of the little insect's energy. It pushes itself out, inch by inch.
The newly emerged Cicada grasps onto the shed exoskeleton and sits there, to allow the blood to flow into its veins, thus gathering strength in its wings and the rest of its body. The brand-new outer covering has a bluish-green colour to it, which gets darker as it thickens, and the Cicada soon regains its original colour.
Having gathered the necessary strength, it is finally ready to fly away into the world with its brand-new look, to discharge its duties as an adult, which, predominantly, would be to procreate. And, this is where their distinct call has a role to play.
Cicadas are more often heard than seen. The males of the species, to be more precise, are the ones capable of making these sounds. However, both sexes have a membrane called the ‘tympana' which aids in detecting sound. The music of the Cicadas has various connotations - distress calls, mating calls, or courtship calls in some species.
Their calls are very loud and sometimes, very high-pitched too. Some Cicadas are capable of producing sounds up to 120 dB; amongst the loudest of all insect-produced sounds. This is technically loud enough to cause permanent hearing loss in humans, should the Cicada sing just outside the listener's ear. Also, some smaller species have songs so high-pitched, that the noise is inaudible to humans.
Cicadas possess an organ called the ‘tymbal' in their abdomens (the orange rings in the image below, which pull up and down while the Cicada calls), which is what they use to generate these sounds. The muscles around the tymbals are flexed, thus pulling them in and out of shape, generating the clicking sound which then gets amplified by their hollow abdomen.
These calls carry to long distances, and also seem to be echoing from multiple directions. Cicadas are like the symphony artists of the forests; large numbers, from many different trees, start calling in unison. This is a wonderful experience indeed. The symphony starts with one call by the lead Cicada, and is immediately followed by many others, resulting in the amplification. There is a lull in between; a complete silence, an interlude of sorts; before the calling resumes in exactly the same manner. This whole musical performance is not just one single, straight note. It is a multitude of notes with a lot of modulations in them as well.
There exists an elaborate pattern of time-sharing amongst Cicada species for this calling, to avoid any acoustic interference with each others' calls. It all seems to so simple at first thought, but holds a great amount of detail when one takes a deeper look. That is the reason they are referred to as songs of Cicadas, rather than just calls.
So, the next time you are in a forest and hear a symphony of clicking and buzzing sounds during the day or at dusk, the artists would undoubtedly be the Cicadas. Just soak in their performance.