Millions of butterflies, including blue tigers, dark blue tigers and crow butterflies, are migrating from the Eastern Ghats towards the Western Ghats during the onset of the Northeast monsoon in October 2026. The movement across Tamil Nadu is linked to the seasonal rains and the availability of host plants in forests of the Western Ghats.
Seasonal Migration across the Ghats
The current migration proceeds westwards from the Eastern Ghats, across the Tamil Nadu plains, towards the Western Ghats. The butterflies move away from heavy Northeast monsoon rain affecting Chennai and surrounding districts. A return movement towards the Eastern Ghats and plains generally takes place in April or May, before the Southwest monsoon.
Butterflies may pause at forest patches during the journey. They feed and reproduce after reaching host plants in the Western Ghats; adult butterflies lay eggs before dying. The next generations make the return journey, with the timing associated with pre-monsoon showers.
Species and Ecological Features
The migrating species include the Blue Tiger (Tirumala limniace), Dark Blue Tiger (Tirumala septentrionis), Common Crow (Euploea core) and Double-branded Crow (Euploea sylvester). Tiger and crow butterflies are among the groups observed during seasonal movements between the Eastern and Western Ghats.
Host plants provide food for caterpillars and support the life cycle of butterflies. Adult butterflies feed, mate and lay eggs in forest habitats after migration. These movements are associated with seasonal changes in rainfall across southern India.
Migration Monitoring and Road Mortality
Active movement was observed on 17 and 18 October 2026 in western Tamil Nadu, including Salem, Namakkal, Erode, Tiruppur and Coimbatore districts. Counts in Coimbatore district ranged from 5 to 135 butterflies per minute at different locations. At Kalapatty Main Road, observers counted 120 individuals per minute on 18 October.
The Nature and Butterfly Society has monitored the regional migration pattern since 2013. Volunteers also use the Butterfly Migration India WhatsApp group to share observations and counts. Many butterflies have been flying close to the ground during the current movement, and road collisions have killed hundreds along routes in Tamil Nadu.
Important Facts for Exams
:
- The scientific name of the Blue Tiger butterfly is Tirumala limniace.
- The scientific name of the Dark Blue Tiger butterfly is Tirumala septentrionis.
- The Eastern Ghats and Western Ghats are mountain ranges separated by the Tamil Nadu plains.
- The Southwest monsoon generally follows the pre-monsoon season in April or May in this migration cycle.
The seasonal westward movement coincides with the Northeast monsoon, while the return movement generally occurs before the Southwest monsoon. The Nature and Butterfly Society has tracked this migration in the region since 2013.
