---

I'm relatively confident that this is Synagris, based at least in part on having seen several males with impressive headgear, but as large and distinctive (and not hugely speciose) as they are, there's not a great deal of information available on which is which.

So, on the offchance that someone here knows a little about large and charismatic potter wasps as well as a great deal about flies, I'm posting it here.

Place: Chongwe District, Lusaka, Zambia.
Habitat: Seen at most locations throughout area - residential, argicultural, and dry scrub - provided water and shade. Dozens congregated in rushes, along at least two large species of Pompiliids, between midday and 3pm.
Date: 04.10.2011.
Size: 3, possibly 4, cm.