Common Windmill Swallowtail
The Common Windmill (Byasa polyeuctes) is the most common member in India of the Windmills genus Byasa, comprising tailed black swallowtail butterflies with white spots and red submarginal crescents.
This butterfly prefers forests and woods. Frequents river valleys. It occurs at low elevations (1000 to 5000 feet) in North East India but is found at higher altitudes in the western extent of its range – up to 11,000 feet in Kashmir.
This butterfly has a leisurely flight high above, but is easily recognisable by the thin long fore and hindwings. It is attracted to flowers and visits Clemanthe, Buddleia, Lantana and Rhododendron blossoms.
It is mimicked by a day flying moth Epicopa (or Epicopia) polydorus, which flies at the same period and over the same range as the Common Windmill and has much the same manner and habits. source