On 5/25, 2 of 5 eggs hatched, the remaining 3 eggs never hatched and remained in the next. So the nestlings are
probably 16/17 days old today. I have been feeding mealworms (in a jail style feeder to prevent large birds from eating them). Parents have been in and out all this weekend. I haven't checked the box for a few days.

This evening for some reason I decided to check the box. To my astonishment, nothing is there, no eggs, no nestlings. Looking around there is NO broken pieces or feathers anywhere. The nest is very neat, nothing is disturbed, see the picture. I do see bluebirds around, they are probably the parents, but they have not taken the mealworms I put out this evening (but mealmorms from this morning were gone)

Could they have fledged? The last couple years, my nestling always fledged at 20 days or later, after lots of peaking, and always left very messy nest. Or is it more likely that predators got them? We have feral cats around, but can a cat leave the nest totally untouched? What is most likely has happened? I am very bumped out, this has never happened in my 5 years of raising bluebirds.