CHENNAI: The prolonged lockdown has given us the perfect opportunity to experience the delights offered by the flora and fauna around us. Along with the petrichor brought by the unexpected showers, one can spot pretty butterflies, dainty dragonflies and the oft-misunderstood moths, flitting away near thickets of bushes and trees. It is during the months of July-September that a variety of moths make an appearance in the plethora of ecosystems that Chennai has to offer.
Tagged as pests by farmers, moths are in fact strong indicators of a healthy ecosystem. To appreciate their presence and the perks they bring with it, naturalists have tagged this week (July 18 to 26) as National Moth Week. “We have over 12,000 species of moth in India. In March 2019, three of us from the Madras Naturalists Society (MNS) set out to study the various species of moths that are habitual to the tropical and estuarial ecosystems of the Adyar Estuary,” says M Yuvan, a naturalist affiliated with MNS, who has studied a few species in captivity to understand their lifecycle and natural behaviours.
They conducted a year-long study and documented 82 moth species in the area. Vikas Madhav, a naturalist and contributor adds, “Multiple groups around Chennai have documented close to 250 species of moths in the city.” With what has been documented so far, we know that most moths are non-migratory. Their life span depends on their size. Larger moths live up to several weeks while the smaller ones complete their cycle within a few days. Yuvan points out that moths pupate under the soil. Unlike their cousins, the butterflies, moths settle in the foliage that coats the topmost layer of soil, during the day. They have been observed to emerge during or after a bout of rainfall.
These nocturnal insects also exhibit a phenomenon called diapause. “It is when the moth pupae go into hibernation while waiting for ideal conditions for the adult moth to emerge,” Yuvan explains. The period of diapause is variable and can go up to a few months as well. All development of the larva is suspended during this time and normal pupae emerge within a week. After spending close to two days to a fortnight in a glutinous egg, newly emerged adult moth larvae sustain themselves by feeding on nearby plants. However, some have restricted dietary requirements. While most moth caterpillars can break down most kinds of plant matter, there are few that can only digest a particular species. Once out of the pupae stage, adult moths lose the ability to regenerate. They have liquid diets like nectar or sugar water, but cannot digest much else. “The life of an adult moth heavily depends on what it consumes as a larva,” he says.