I can only ID this to genus Heptagenia, which is is a genus of flatheaded mayflies in the family Heptageniidae. There are are a few different species in Heptageni. Mayflys only have a very short life, and are well known to fly fisherman who make their lures to resemble these lovely delicate insects. I found this one at night near a catchwater on Tai Mo Shan a few weeks ago, in May.
