This was the first chickadee nest I had ever seen and yes, it was very pretty and delicately made.
As a side note, the nest was infested with tiny ants, you don't suppose that that was what caused the chickadees to leave do you?
I would doubt it was the ants. More likely a predator bird, wrens are good culprits. Sometimes checking a nest box too frequently can scare them off. I never look in mine anymore, just clean them out in the fall and early spring. Sometimes mice like to make a winter nest!