This dark beetle is Paropsisterna nigerrima var. picta. The structure is identical to the common striped form but the color pattern is different. The important srtuctural feature to note for ID is the fine striae (puncturation lines) along the elytra. Sadly, the color patterns are no help. The third variety (nigerrima nigerrima) is entirely black. I suspect that at least two more variations occur that are not recorded in the MOV collection. One is entirely light and dark banded, the other is from NSW and has a different red spot pattern.
This fly has been identified as Exaireta spinigera (family Stratiomyidae), by Ken Walker. But - it has also been identified as being of family: Therevidae and in sub-family Agapophytinae by Tony Daley. I am unsure which identification is correct, but from my limited resources (photos in books) it does look like Stratiomyidae.