Regarding pill bugs/sow bugs/woodlice http://davesgarden.com/guides/bf/go/142/ and nestboxes, chances are that if you have them in the box then the box is not dry. Pillbugs are found in humid and dark conditions such as wood piles and compost heaps. They also feast on wood. If you have these in the house, then check the house for needed repairs. If you have a nest and/or babies currently, then add some grass to keep the nest dry or hypothermia might be problematic http://sialis.org/hypo.htm.
In relation to bluebird diets, I'm not sure that bluebirds would eat these normally since they are undercover. Members of the Bluebird Box have cited collecting these and using as an emergency food source, though there is also some chatter that this bug might carry a parasite harmful to fledglings. Best to stick with mealworms!!