They resemble a stream — millions of blue tiger and glossy tiger butterflies snaking their way through the Western Ghats. They move swiftly to an unknown destination. Recently, they crossed Agali in Kerala, and Anaikatti and Sathyamangalam in Tamil Nadu, much to the delight of Nature lovers. Butterfly migration is noticed during the South-West and North-East monsoons in Tamil Nadu, Kannur and Silent Valley in Kerala, Bandipur in Bangalore and parts of Andhra Pradesh. Even today, this fascinating phenomenon intrigues naturalists. “We have more questions than answers,” says P. Pramod of SACON. What is the trigger? How do they survive? Where do they start? “An adult larva requires a minimum of three to four leaves to survive. It’s not clear how they manage the food requirement. The presence of butterflies is an indicator of healthy vegetation in the eco-system,” he says.
Naturalists say that this year, lesser number of butterflies were sighted. And, it was predominantly the blue tiger. “A few years ago, we saw over six species such as common crow, double-banded crow, lime butterflies, common albatross and leopard. And in the months of June and July, we sighted the common emigrant butterflies. We have not seen much activity in the last three or four years,” Pramod explains.
Birder P.R. Selvaraj of Coimbatore Nature Society spotted hundred of butterflies near his house in Peelamedu. “More than 500 butterflies kept moving towards the West and disappeared in a flash,” he says. Another Nature enthusiast, A. Sukumar, spotted butterflies in flight at Pankaja Mill Road. “After the monsoon, they start moving to bask in the sunshine.”
Butterflies migrate because of climate change, to seek food or for mud puddling, where male butterflies extract minerals and water from the wet soil that they transfer to the females during mating. “In some cases, it may be a mere dispersal to cope with food scarcity. For instance, the life of common grass yellow butterfly revolves around kani konna, whose leaves they feed on,” says Sukumar. He mentions the migration of pink rose and crimson rose butterflies from Kanyakumari to Sri Lanka. “They resemble a pink line dotting the sea. There is also altitude migration seen in the Himalayas among butterfly species such as blue mormon, large cabbage white and painted lady. When it rains, they descend to the foothills for sunshine. As butterflies are fragile, it is difficult to tag them for research. What is possible is adding a micro label to the forewing.”
Birder R. Mohammed Saleem of Environment Conservation Group says every butterfly species has a specific host plant. “For plain tiger butterflies, it is milk weed. The caterpillar feeds on the poisonous leaves and the butterflies, in turn, carry the toxic content in their body. This protects them from being preyed upon by predators. During migration, they settle down on moist soil for mud puddling and move in colourful groups.”
Observe Nature
G. Parameswaran, a bird watcher for 20 years, says there are many theories for migration, all worthy of future study. “During the caterpillar stage, they can sense how much food is available in a certain location. Based on that assessment, adult butterflies migrate.” This migration, he says, is a great opportunity for youngsters to observe butterflies and moths. “A much better sight than anything on TV,” he says.
The monarch butterfly migration in the U.S. is well-recorded. It occurs over the life span of three to four generations as they migrate southward during late summer from the U.S. and Southern Canada to Mexico and coastal California and return in spring.
In India, we have only a few anecdotal observations. The migration pattern follows a heavy, directional flow. Every minute, hundreds of butterflies cross from one direction to another and this continues for a week. As butterflies have a short life span of two months, it’s always new offspring that returns after a migration.
Pramod recalls a memorable sight. “Lemon butterflies and tigers look like a river in motion while the common albatross (white) move in a line. I remember seeing an endless white line stretching to many kilometres in the Kannur forest. It was fascinating.”
