Byasa polyeuctes, the common windmill, 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 lives in Pakistan, northern ranges of India, Nepal, Bhutan, Myanmar, northern Thailand, Laos, Vietnam, southern China (including Yunnan) and Taiwan.

In India, the Himalayas from Himachal Pradesh to Sikkim, Assam onto Chinese South Tibet region and northern Myanmar.

This butterfly has a leisurely flight high above, but is easily recognisable by the thin long forewings and hindwings.

It is attracted to flowers and visits Clemanthe, Buddleia, Lantana and Rhododendron blossoms.