This is an interesting little taxon shaped a little like a queen wood ant, with a very bulbous abdomen. The basic colour is glossy black with quite a dense layer of hairs on the abdomen. The head is quite rounded – especially at the back, with long antennae and a yellow arista.
EDIT (Monty Wood 26/9/2010): This is a fly that is closest to Itacuphocera sp. but may belong to 2 other very similar genera – or an entirely new one.