If you’ve been spotting more butterflies than usual in Chennai lately, and have been keeping an eye on the news, you’d know that thousands recently migrated to north Tamil Nadu, riding the wave of the south-west monsoon. But these delicate creatures are more than just fleeting bursts of colour. Butterflies are complex and little-understood indicators of change. With every flutter, they reveal more than what meets the eye — signalling weather shifts before our forecasting systems can, and silently reminding us of our changing natural landscapes. But to truly understand what they’re telling us, we need to stop, watch, and care enough to listen.
From shedding light on migration patterns, how butterflies can become ecological indicators to exploring whether Chennai offers enough conducive habitats for butterflies, author of Intertidal, and naturalist Yuvan Aves weighs in on these tiny marvels.
Excerpts:
What species of butterflies were seen during the recent migration in the city and is it a regular event?
Butterfly migration happens every year, but last year there was no great spectacle like this. In fact, in the last four to five years, when I have been very keenly watching them, I haven’t seen such a large migration. This July, the butterfly species migrating in greatest numbers were the Blue Tiger, the Dark Blue Tiger, the Glassy Tiger, and the Common Crow. Along with them, maybe one in a hundred or thousand, were Common Rose, Common Emigrant, and even the Southern Birdwing — India’s largest butterfly — was spotted in Besant Nagar, but sparingly. All of them were moving from the Western Ghats to the Eastern plains due to the south-west monsoon and around November and December, when the north-east monsoon sets in, they return. Some species of butterflies have adapted to stay in the Western Ghats even during torrential rains, while the others have preferred to move as always.
But this isn’t the first group to migrate this year. The Common Emigrant migrated in the first week of June here. It was prominent but not many media houses covered it. Earlier this year, in January, Kerala witnessed the Common Albatross migration at Aralam Wildlife Sanctuary. It was so large that the Kerala government made it the first butterfly wildlife sanctuary in India. But it is interesting to see two back to back massive migrations this year in the South.
How do butterflies navigate and migrate?
Before migration, butterflies congregate in very large numbers. In forests, the Blue Tigers, and Common Crows especially, congregate on hanging vines, on aerial roots, on Banyan vines, and Tenespora. They congregate in thousands.
They then have a specific order of migration. We did a bunch of surveys in Guindy National Park in the first week of June and found that the Common Emigrant was migrating in very large numbers, using very specific corridors. They may use the beach, railway tracks, and highways to fly passively and let the winds carry them, especially those corridors that run West to East or South to North. To determine the direction of travel, they are using a very complex internal system called the time-compensated sun compass [a complex navigation system used by migratory birds and animals]. As the rain picks up more and more, the Blue Tigers, also called milk-weed butterflies, and Common Crows start to migrate.
What is also interesting is how they use the gaps in the Western Ghats to avoid flying over high mountains. They use the gaps in Palakkad and Sengottai, and migrate passively with the winds. In Chennai’s coast line, two weeks ago, one would have noticed sixty to hundred butterflies a minute over a 20-metre transect, using the south-west breeze to come to the shore and find habitat.
Different species have different ways of migrating. For instance, we can understand cautious and audacious migrations through the Common Albatross and the milk-weed butterflies. The former species is edible and is food for birds. So they migrate in a single-file formation along the river. This gives them protection and is understood as a cautious migration. Milk-weed, on the other hand, is poisonous; they eat poisonous plants. They migrate however they deem fit and therefore, I use the word audacious, because no bird would dare to touch them.
What does their migration indicate, barring it being seasonal?
Butterflies’ hygrorecepting abilities — sensory receptors that can detect changes in the weather such as moisture level and humidity — paired with their migratory patterns, can indicate weather changes that our advanced weather equipment may take a while to pick up.
The kind of migration we saw this July, can typically be a sign of an upcoming intense monsoon. Migration, of course, happens when rainfall is is high but usually they are signs of an intense monsoon. I remember 2015 very clearly when butterfly migration was massive and we experienced intense monsoons. Linking such large migrations to intense monsoons is echoed in British naturalists’ observations as well.
A lot of work on understanding butterflies as weather indicators is emerging. For instance, Monarch butterflies in the US are getting more tired, splitting the population because of the changing climate. The climate change there is changing vegetation patterns. A lot of such work could be replicated here too for us to improve our understandings further.
How are butterflies considered as ecological indicators?
Each species of butterfly has a specific group of host plants. The Common Crow, for example, are dependent on the Oleander plant; the Tawny Coster in Chennai are dependent on white buttercup and passion vines. If these plants didn’t exist, these species would perish. The presence and diversity of butterflies, therefore, give a very good understanding of habitat health, forest health, vegetation, and diversity. For example, rich presence of Lianas typically indicates old growth forest and if lots are there and feed on Lianas, you can say that the forest is in good health. Similarly, if you spot the Glad Eye Bush Brown, it indicates good undergrowth and good soil health.
A book titled Butterflies on the Roof of the World: A Memoir by Peter Smetacek talks about how Golden Birdwing butterflies can tell if there is ground water or not. This species feeds on a particular type of plant that can grow enough pods only if the water table is high. These are the reasons why we call them ecological indicators.
Have there been any massive changes in the local habitat for butterflies in Chennai?
Butterflies draw salts from mud puddles. They do this along river beds, lakes, and wetlands. The salts it accumulates are very important as male butterflies offer these salts as nutrition to the female butterflies for procreating. As our landscapes change, rivers and wetlands are invaded upon, butterflies are being denied nutrition.
Then there is also the changing vegetation in Chennai that affects butterflies. The Blue Tigers, for instance, eat specific plants, because in adulthood, the male butterflies need a set of chemicals to produce sperms. For this purpose, they seek Heleotropium and Crotoleria, which are not found abundantly. If people manage to spot these plants in our city, they will notice an explosion of butterflies. So, the specificity of plants makes them susceptible to habitat loss.
The reverse has also happened. Common Jay and Tailed Jay were not common 10 years ago in Chennai. But they are abundant today due to the rampant planting of the false ashoka by the GCC. Even the other varieties that are being planted in our city’s parks are manipulating the habitats of our insects and don’t allow for butterflies to proliferate.
How have steps to conserve butterflies panned out so far and what can local communities do?
Insect conservation has not caught up with larger wildlife policy yet. I was conversing with late Dr Parthiba Basu from the Centre for Pollination Studies, before his unfortunate death, and he mentioned that our fruit and vegetable yield is plummeting due to pollinator decline. He explained how our food and nutritional security is linked to insect pollinators. But these are not findings enough in larger policy spaces.
On a city-level, if the Corporation takes an initiative to plant the right vegetation in just about 10 spaces to support as many species of butterflies as possible, people will be able to spot them, witness their lifestyles, and maybe grow fond of them.
As for local communities, before the aspect of care, comes connection. They should connect, learn, understand, and eventually appreciate what butterflies do in our ecosystem.
Lifespan trajectory
Most butterflies live for just a few weeks, though some migratory species survive for months. Studies show their lifespan depends on species, climate, and habitat conditions. According to Yuvan, there is a new and emerging study by PA Vinayan, who is placing small transmitters in butterflies’ wings to understand their migration patterns. He is expecting the study to make new revelations about the life-span of several species here.