Males and females upperside deep indigo-blue black; a postdiscal slightly sinuous blue band crossing both fore and hind wings
Very widespread from South Asia to Japan with a number of well marked geographic races.
This butterfly has seen better days. It landed on my backpack while I was photographing butterflies on a sandbank beside a small stream in Nam Nao national park. I have seen many Red Admiral butterflies this spring near where I live. I didn't know there was a Blue Admiral.