Why Chennai should keep an eye on moth cocoons


You might have noticed plenty of moth larvae and cocoons around you lately. Here’s why they are important, and why you should not hasten to get rid of them

As rains recede from Chennai, so do the moths.

While many might consider this a good thing — some moths are, after all, pests that put plants at risk — city naturalists say the winged creatures have more to offer than they are given credit for. Indeed, we owe much of the region’s flora to certain moth families.

“Moths are much more cryptic than butterflies; many of them are nocturnal, and some don’t leave the shelter of their plants. So, they are difficult to study and not much is known about them. Even though there are 12,000 to 15,000 species of moths in India on an estimate, a lot of them are undocumented,” says city-based naturalist and author M Yuvan.

He, along with fellow enthusiasts from Madras Naturalists Society, recently decided do something about this — an innovative experiment that they have been working on for about 10 months. Moths, explains Yuvan, are attracted to ultraviolet light. So the team developed simple “moth screens” comprising a white screen lit by ultraviolet light to lure the creatures into the open. “They settle on the screens for a while, giving us a chance to identify and observe them,” says Yuvan.

This method led to a rather surprising realisation: “In Adyar Poonga, we observed that a lot of them are host plant-specific. The lunar moth, feeds on a handful of trees like the Arjuna. Emerald moths feed on oaks, and oleander hawk moths prefer the oleander plant.”

This was a pattern they noticed during their trips to other parts of the country as well. The brilliantly-coloured cyara genus of moths, endemic to the NorthEast, feed only on oaks. Even the neem tree, famous for its properties as a natural pesticide, has a moth exclusive to it: the geometric moth. “There is almost no tree or plant that does not have a moth associated with it. Even the poisonous milkweed has moths living on it; they sequester the poison instead of digesting it, thus becoming poisonous to predators.”

Why should we care? Because this relationship between fauna and flora affects not only the greenery around us, but also the birds we see flitting about. “Hawk moths, for instance, are very important pollinators for flowers that have a long corolla,” says Yuvan. These include a number of the deeper flowers found in and around the city, which depend entirely on the hawk moth family with its long proboscis for reproduction and survival.

An example would be any among a large number of orchid species found across the Western Ghats and Northeast India. “The hawk moth-orchid relationship is a famous one in evolutionary biology,” says Yuvan. And then there are the bellflowers, and the night-blooming snake hemp plant, whose leaves are so upright and tall that only hawk moths can reach in to pollinate it.

Birds have a lot to be grateful for, as well: “Caterpillars and moths make the bulk of larvae in any habitat, and comprise the maximum food for birds and insects,” says Yuvan.

These are patterns seen everywhere; every 100 metres or so within Chennai city, exists such an ecosystem surviving on its own. But for the naturalists, this study is not just about natural dependency and survival patterns. It also revolves around the simple fact that, regardless of how little we know about them, moths are interesting and beautiful.

“A lot of them have interesting features. Some moths have a face pattern on their wings, complete with eyes, to startle predators. And we have all seen moths that mimic leaves, and others that mimic the bark of trees,” says Yuvan. He adds, “There is also a third kind: a moth that mimics dappled sunlight.”

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Printable version | Jan 23, 2020 1:03:23 PM | https://www.thehindu.com/sci-tech/energy-and-environment/why-chennai-should-keep-an-eye-out-for-moth-cocoons/article30523553.ece

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