large red-bodied Swallowtail
It is widely distributed in Asia. Afghanistan, Pakistan, India(includes Andaman islands), Nepal, Sri Lanka, Myanmar, Thailand, Japan (south-western Okinawa only), Laos, Vietnam, Kampuchea(now Cambodia), Nicobar islands, peninsular and eastern Malaysia, Brunei, Philippines (Palawan and Leyte), Indonesia, and Taiwan.
I watched this butterfly fly around for at least 15 minutes. It hardly ever landed and stayed still. I kept waiting and watching. These were the best shots I could get of it.