The Chinese Windmill (Byasa plutonius) is a butterfly found in Asia that belongs to the Windmills genus Byasa, comprising tailed black swallowtail butterflies with white spots and red submarginal crescents.
The two subspecies in the Indian subcontinent have the common names of Pemberton’s Windmill and Tytler’s Windmill.
Wingspan : 100 – 120mm.
Tail black in both sexes.
Male – Above, brownish black and unmarked except for a row of markings.
Pemberton’s Windmill (Sikkim-Bhutan) – This row from veins 2 to 6 on the upper hindwing consists of whitish marginal spots.
Tytler’s Windmill (Manipur, Naga and Chin hills) – This row consists of prominent black marginal spots on the upper hindwing and small red spot in vein 2.
Female – Above, paler. The female has traces of red lunules on the margins from veins 3 to 6 on the upper hindwing. source