That's a new one on me.

After living in Penrith since 1978 we finally went for a bit of a wander along the River Eamont.
We kept seeing what looked like black-winged mothy sort of things along the bank. Eventually one or two condescended to sit still for more than a handful of nano-seconds and we discovered that it was a black patch on every wing creating a strange moth-like flap, unlike the helicopter-like motion we're used to in "yer average" Dragon/Damsel Fly.