Black-banded Gossamerwing (Euphaea decorata):

The Black-banded Gossamerwing Damselfly can be found near most mountain streams throughout Hong Kong. The male is characterised by it's black band across it's wings, as shown in the picture below. The female does not have this distinct black band, rather the front of it's wings are pale brown.

The difference between a damselfly and a dragonfly is that a damselfly is typically smaller and will fold its wings parallel to its body when at rest, whereas a dragonfly will be bigger and have it's wings open when at rest.