Wow, that's a YOUNG bird. I've never raised one that young before.

What, and how, you feed a baby bird is VERY dependent on the species of bird.

For example, I have raised a lot of baby pigeons. They pretty much drink formula from a bottle, much like a mammal would. They thrive on commerical parrot hand-rearing formula, and are quite hardy and easy to keep.

I have raised several starlings. Starlings are primarily insectivores, so their diets consist of mostly protien. Baby starlings are easily raised on soaked dog food, placed in the back on their mouths with tweezers.

Trying to feed a pigeons diet to a starling, or visa versa, would surely kill them. Just as cats are carnivores and horses are herbivores ... some birds eat strictly fruit, some seeds, some insects. It's very important to know what type of bird you have. Worms aren't really a good idea for a lot of species of bird. While some birds, like robins, sometimes eat earthworms, it is not their primary diet. Feeding an earthworm to most baby birds would be like trying to feed a human baby a T-bone steak.

Just by looking at his feathers which are starting to come in, could he perhaps be a bluebird?

I would really look for a licensed wildlife rehabber, who can identify the bird for you.