what do you feed earthworms?

Answer 1

"many forms of organic matter in soil, things like decaying roots and leaves, and living organisms such as nematodes, protozoans, rotifers, bacteria, fungi"

If you maintain a compost pile, you may find them constantly invading it.

Newspapers in dirt might be enough, but they need a few vitamins too. . .

Answer 2

compost/dirt. Nothing acidic like orange peels, lemon rinds etc.