Bluebirds don't generally visit your regular seed feeders.  They perfer insects and fruit.  You could feed them dried fruit such as raisins, dried cranberries, grapes, pieces of apple or bananas.  Providing mealworms for them would be a treat.  Bluebird feeders allow you to place fruit and insects into a confined area that only bluebirds would like to eat from.  They generally have clear plexiglass on 2 of the 4 sides with holes on all 4 outer walls, allowing easy entry and exit of the bluebird.  Most other birds would not want to be constricted like that, but the bluebirds think it's really great!  This is a perfect way to be select in your feeding and especially allowing bluebirds, rather than other critters, access to the food.  If the mealworms are live, they will not be able to crawl out of the feeder.  We carry dehydrated mealworms in the store for your convenience.