Coimbatore: As bustling city streets mark festive holidays below, a remarkable natural spectacle unfolds overhead as hundreds of thousands of blue tiger, dark blue tiger, and common crow butterflies take to the skies. This movement signals the start of the annual migratory season, with insects flying from the Eastern Ghats toward the Western Ghats to avoid the heavy downpours of the North-East monsoon battering Chennai and surrounding districts.
Butterfly watchers across Salem, Erode, Tiruppur, Coimbatore, Madurai, and parts of Kerala have been placed on high alert, coordinating through regional networks to count and monitor the passing insects. According to core members of The Nature and Butterfly Society, specific locations in Coimbatore recorded between 100 to 120 individuals passing per minute during peak observation times, featuring a mix of blue tigers, dark blue tigers, common crows, double-banded crows, and emigrants.
Experts explain that the insects undertake this arduous journey to escape the heavy rains and locate host plants deep within the forests of the Western Ghats. Dr Kalesh Sadasivan, a research associate with the Travancore Nature History Society and a state wildlife board member, notes that the migration begins following pre-monsoon showers in the Eastern Ghats, taking the butterflies across Tamil Nadu plains and the Mysore plateau. Upon reaching their destination, the insects feed, mate, lay eggs, and ultimately perish.
The subsequent generations, potentially the third or fourth offspring, make the return journey back to the Eastern Ghats around May when pre-monsoon showers precede the South-West monsoon. During the intervening months between January and February, millions of these butterflies congregate on trees in deep forest sanctuaries such as Parambikulam and Silent Valley, waiting for environmental cues encoded in their DNA to signal the return flight.
Conservationists emphasize that the migration relies heavily on clear skies with minimal cloud cover. The butterflies do not fly continuously, choosing instead to settle on trees to rest by mid-afternoon before resuming their journey the following morning. Under optimal sunny conditions, thousands can be observed crossing a given stretch within an hour.
Researchers underscore the ecological importance of tracking these patterns, noting that butterflies serve as critical indicators of a healthy environment and form a foundational part of the local food chain. Organizations like The Nature and Butterfly Society continue to contribute crucial baseline data through systematic checklists and surveys conducted in collaboration with forest departments across the region.