Eastern Bluebirds eat many different types of fruits, nuts, seeds, and insects. Some of their favorite things to eat are mealworms, crickets, grasshoppers, flies, and other soft insects. They will eat berries off trees, bushes, vines, and other various plants. They also eat sunflower seeds, and even suet. Although if you really want to give them a treat raise or purchaise some mealworms.