I thought this was a bee or wasp of some sort, but after looking it up I've discovered that its a Mydas Fly.

It looks as though I'll be getting more of them, given what this pair on my Cassia are up to.

I don't think any flies can eat solids; they slurp liquids, so that Mydas Fly on the Spanish Needles flower above must be sipping nectar. That is one popular flower in the world of butterflies and bugs!

As I see more, I'll add more. You might want to have a look at my Wasp page; at the bottom of it there's a picture of a wasp that I think is chewing on a Mydas Fly.