In this one the youngster has just been fed a Brimstone moth.
The adult is carrying a ring and I assume it is probably this individual we ringed in the Magic Garden in the spring.
Spot Flys often nest in close proximity to people, for example in vegetation on buildings or holes in walls. In fact one of the old local names for the species was the rather lovely Wallchat. One pair a few miles from here took this to an extreme by choosing to nest on the hinge of a gate to a tennis court. This gate was in constant use through the summer but the pair still managed to raise their brood.