CHENNAI: In a vivid natural spectacle, millions of milkweed butterflies are sweeping Chennai, turning the city’s skyline in many parts into a fluttering canvas of black and blue. This phenomenon, one of India’s least understood yet most magnificent animal migrations, is tightly linked to the rhythm of the monsoons.
To watch this, visit any beach in Chennai by noon to find thousands of butterflies moving in small groups. Triggered by the intense southwest monsoon rains lashing the Western Ghats, butterflies like the Blue Tiger and Common Crow are migrating northeast, away from their saturated breeding grounds to the eastern plains.
These migrations are part of a rare bi-directional pattern and the butterflies return westward during the northeast monsoon. “These movements are biologically significant, as the butterflies are escaping inundated habitats and likely heading to drier areas,” experts say.
Naturalist Yuvan Aves said the butterflies are highly sensitive to environmental cues like wind speed, humidity and temperature, and this year’s intense early rains and cooler temperatures may be amplifying the migratory wave.
“During years when intense monsoon is expected, usually the butterfly numbers are very high. This seems to be one such year. Recently Bengaluru experienced a similar mass migration in May, ahead of the monsoon’s formal onset.”
Interestingly, many butterflies leverage prevailing winds to glide over long distances. Increasingly, they are seen using roads, rail tracks and even flyovers as directional guides during their journey. These migrations, scientists believe, could serve as natural proxies to understand monsoon behaviour and help track climate shifts.