Bluebirds' favorite food of all... live mealworms! Sometimes it's the only way to actually attract blues to your place. The creepy crawly part isn't so bad, it's easy once you get the hang of feeding and handling!
The worms are fairly inexpensive when purchased in bulk... it's the overnight freight that hurts! So the more you can buy-the less expensive they are. Some folks even grow their own worms, but it's a very time consuming project requiring great patience. Wouldn't you rather spend that time bird watching?
Here's easy info with the 3 required items and best storage for your meal worms. And don't worry too much about the fridge... worms transition to a dormant state once chilled so they're no longer creepy crawly :)