Sounds of cicadas: A loud but under-studied insect is finally getting attention

On a wet rainy day in 2014, Kiran Marathe was busy looking for loud, clamorous cicadas hiding in the bushes, in Verlem district in South Goa. Marathe, a young 20-something researcher from the National Centre of Biological Sciences, Bengaluru, works on one of India’s most under-studied species of insects – the cicadas. Since 2013, he has been combing the Western Ghats looking for cicadas.

On June 16, 2014, in Verlem, on his trail in search of loud cicadas, Marathe heard a feeble “crick” like sound. “I was intrigued because it sounded like a cicada but not loud enough,” he said. A little bit of poking around revealed a really tiny cicada. At first he saw only one, but soon enough found several of them on the undersides of leaves on bushes.

It was raining and Marathe’s field equipment was refusing to comply. His camera wouldn’t switch on and unfortunately he did not have a sound recorder with him that day. He could take no pictures and record no sound, but he did manage to collect several samples of the tiny cicada.

Anatomical studies of the samples revealed the tiny cicada to be a new species that Marathe and his colleagues named Rustia minuta, on account of its small size.

Fast forward three years from that day in Verlem, Marathe and his colleagues found another new species of cicada in July 2017, this time in the Honey Valley estate in Kodagu (Coorg) district of Karnataka. Again a small cicada, but bigger than the Verlem variety and definitely much louder, this new species was named Rustia kodagura.

‘Perfect’ insects

In taxonomic terms, cicadas are ‘perfect’ insects. They belong to the same family of insects as aphids and leafhoppers. They vary widely in size, from really small varieties like Rustia minuta measuring 9-10 millimetres​ in length to varieties that can measure up to seven centimetres long.

Their life cycles can be annual or periodical, meaning some live and die across a span of a year, whereas some others live for a longer period, spread across several years. In either case a large part of the life cycle is spent under the ground in nymph stage. It is only when they are ready to metamorphose into an adult that they emerge from the ground.

All known Indian cicadas are annual, except for one – Chremistica Ribhoi of Meghalaya. Found in Ribhoi district of Meghalaya, after which they are named, these cicadas are locally called Niangtaser and are a part of many legends. According to one of them, Niangtaser was actually an old woman from a village who turned into a cicada. Another legend says that the Niangtaser cicadas commit mass suicide by drowning themselves in fast flowing rivers, as they are attracted to the rushing sound of fast flowing rivers.

Myths and legends aside, this Cicada is most famous for its periodic life cycle spread across an interval of four years. Strangely, their periodic emergence is in sync with the world cup football tournament, which also happens every fourth year. No wonder, they are called the “world cup” cicadas.

The song of cicada

The most defining feature of cicadas does not lie in its morphology but in the sound they make. The cicada’s song has captured the imagination of many poets and writers. Even researchers studying them follow the trail of their sound to locate them.

The sound is produced exclusively by males, who sing to attract female partners. Cicadas don’t sing like humans do with their mouths. Instead, they use specialised structures called tymbals on each side of the abdomen to produce their characteristic sounds. The tymbals are thin membranous structures streaked with marginally thicker ribs.

Repetitive vibrations in the tymbal membrane result in sound. When the membrane buckles, the ribs are drawn inwards and together. And when the membranes are let loose the ribs spread out again. Cicadas repeat this movement 300-400 times per second to be able to produce their characteristic sound. Each species has its own specific call.

Apart from its role in mate finding, the collective sound of cicadas acts as a “very good indicator of forest health,” said SR Hajong of North Eastern Hill University, Shillong. Hajong has been studying the cicadas of the northeast for a decade now. He was the one to first describe the world-cup cicadas.

Some scientists are beginning to build acoustic indices to measure the health of biodiversity. The cicadas with their loud calls are an important component of the soundscape. Hajong too hopes to create such acoustic indices to assess the health of forests in the northeast India where he works.

India’s cicadas

Marathe’s work and the discoveries have finally broken a long spell of disinterest in Indian cicadas. Known for their enigmatic life cycles, a large part of which is spent under the ground, cicadas are easy to find – especially if you follow the trail of their sound.

Approximately 250 kinds of cicadas are known to occur in India. They are distributed across many genera and Rustia is only one of them. However, our understanding about Indian cicadas is next to negligible. Part of the reason is that very little effort has been put in studying and documenting these insects post independence.

Marathe is part of a lab at National Centre of Biological Sciences, headed by Krushnamegh Kunte, where an inventory of Indian cicadas is being compiled. All the pre-independence era data on Indian cicadas is now stored in the Natural History Museum in London. Wanting to make this data available to the Indian research community, Kunte partnered with Benjamin Price of Natural History Museum, who then painstakingly photographed all the specimens of Indian cicadas stored at the museum since the colonial era.

A total of 281 species were photographed/digitised, of which 189 were from present-day India and Bangladesh, 19 from Bhutan, 81 from Myanmar, 46 from Nepal and 22 from Sri Lanka.

All of this information is now available on the website indiancicadas.org. The website is structured as a citizen science initiative where both researchers and non-researchers are encouraged to deposit more data on sightings and other natural history related information on Indian cicadas.

The start of a new relationship

As we begin to learn more and more about the Indian cicadas, gaps in our knowledge about this enigmatic species of insect are getting filled and myths are getting shattered. For example, Marathe’s work has shown that a genus of cicadas called Gudaba is actually redundant and should be merged with the Rustia genus. Both the genera were created almost a century ago but only now with the recent research the lack of any difference between the two has become apparent.

And then there is the case of Silent Valley. The story goes that when the British discovered the area that is now called Silent Valley National Park, they found it to be completely devoid of cicada sounds. They found the region to be so quiet that they even named it Silent Valley. Marathe, however, disagrees with this theory. “It is not true,” he said. “The silent valley has cicadas! The British must have gone there when cicadas weren’t around!”

Who knows how many such taxonomic errors and myths will be debunked as we find more about these insects and learn to keep our ears open and alert for the cicada’s song.

This article first appeared on Mongabay.