With the North-East monsoon setting in, blue tiger and dark blue tiger butterflies in their millions are moving from the Eastern Ghats to the Western Ghats. The swarms also include common crow and double-banded crow butterflies; the blue tiger's scientific name is Tirumala limniace. They avoid heavy monsoon rain and seek forests with host plants to feed, mate and lay eggs. Their offspring stay in the Western Ghats and return eastward around May, before the South-West monsoon. Big gatherings were seen at Coimbatore, Salem, Erode, Tiruppur, Madurai, Silent Valley and Parambikulam, and citizen groups are recording the movement.