The Ghost Swift

This is a female Ghost Moth that came to my window last night. THe male of the species is pure white. Males come together, sometimes in large numbers, at twilight and hover above a patch of grass swaying rhythmically as if tethered like a kite to the ground. Whilst doing this they give off a pheromone that is supposed to smell of male goats (although I've never noticed this). The smell is apparently attractive to the female.
It is the sight of the males swaying in the twilight that gives it the name Ghost Moth. I prefer its Victorian name of The Ghost Swift!