#1
I do not mean the spider nor the fly, look at the larva at the bottom. Crab spider catch only fresh, moving flies so it is not a saprophagouds larva, maybe a parasite living the host like rats leaving a ship that is sinking?
#2
I'm not aware of any cylclorrhaphous larvae that parasitise adult calypterates, so my guess is that the calliphorid prey had some "ready-to-lay" maggots which have deserted the sinking mother-ship.
Whatever is happening, it's an interesting photo!