Wrack-fly Fucellia tergina (Anthomyiidae), Alum Cliffs, Taroona, Tasmania, May 2015
Mass of Kelp Flies (Chaetocoelopa sydneyens) on rocks just above high tide at Muttonbird Island (Coffs Harbour) on the north coast of NSW Australia.
An interesting little beast that first appeared on an inside window, then flew off and later appeared dead inside. I've only found one of these before. Somebody contacted us almost the same day asking about one she had found too.
I think this is Chyromyia sp, but it doesn't come up on iNaturalist.