Southern India witnesses a spectacular natural phenomenon twice every year: the migration of milkweed butterflies. These striking insects travel between the Eastern and Western Ghats, covering distances of 300–500 km, timed with the rhythms of the monsoon.
Scientists say the unique topography of the Indian peninsula and the dual monsoon system are key drivers of this extraordinary movement. Of the ten milkweed butterfly species recorded in the region, six have been documented as seasonal migrants.
As pre-monsoon showers arrive in April, the Western Ghats erupt in blooms. Triggered by the sudden burst of nectar sources, thousands of milkweed butterflies rise into the skies and head eastward, towards the Eastern Ghats and the Coromandel coast. Later in the year, when the northeast monsoon drenches the east, the butterflies make their way back to the misty forests of the Western Ghats.
This migration has been observed for centuries. In fact, British naturalist E.H. Aitken described it in 1897, noting how dense swarms made it impossible to look outside without seeing butterflies in flight. Unlike the North American monarchs that cross 5,000–6,000 km, South India’s migrating milkweeds travel shorter distances, yet their synchronized movements remain equally captivating.
Scientists and Enthusiasts Track the Flight
Butterfly watchers and naturalists have long been fascinated by this migration. In Wayanad, Kerala, some enthusiasts have even followed swarms in vehicles, tracking their steady eastward movement across forests and plains.
Researchers have identified six main species that undertake these journeys, including the dark blue tiger (Tirumala septentrionis), the blue tiger (T. limniace), the common crow (Euploea core), and the striped tiger (Danaus genutia). During migration, female butterflies enter a state of “reproductive diapause,” diverting energy from egg-laying to muscle development, which strengthens their flight for long distances.
The Role of the Ghats
The Western Ghats play a critical role in this cycle. The mountains, ranging from 900 m to over 2,500 m, host diverse habitats and food plants essential for the butterflies. When the southwest monsoon brings heavy rains between June and September, conditions are unsuitable for flight. The butterflies then move eastward, breed, and later return as conditions improve in the Ghats.
Back in their mountain homes, they gather in massive congregations, clustering in shaded evergreen forests, sometimes in tens of thousands. These gatherings, resembling hibernation, can last months and help them conserve energy until the next cycle begins.
Threats to the Migration
Despite their resilience, migrating milkweeds face mounting threats. Habitat loss, pesticide use, fragmented food sources, and climate change are reducing their numbers. Highways and rail tracks also pose risks, since butterflies typically fly just one to four metres above ground. Ironically, highway plantings of Nerium oleander, a host plant, attract them towards busy traffic zones where many perish.
Conservationists warn that protecting both breeding grounds and congregation sites is crucial. Like the monarchs in North America, these Indian butterflies depend on multiple habitats across vast landscapes, making their survival highly vulnerable to environmental disruptions.
A Lesser-Known Marvel
Though less publicized than the migrations of monarchs or painted ladies, South India’s butterfly migrations remain one of the subcontinent’s most remarkable natural spectacles. Each year, as the monsoons dictate the rhythm of life, these delicate fliers continue their timeless journey between mountains and coasts a silent reminder of the fragile balance between climate, landscapes, and wildlife.