Insects and nestboxes
Bees, wasps or earwigs will, on occasions, take over nestboxes and there is little one can do to prevent it – apart from using insect sprays. As many of the insects are useful food for birds, it is best to leave them alone. Insects often move in after birds have finished nesting. Any young found dead are likely to have died of other natural causes.
It is not unusual for the same type of insect to return to the box in subsequent years. Leave that box in situ and put up another one a few feet away. It is rare for both to be lost to insect invasion.