Can earthworms eat sawdust?

Yes, according to The Earthworm Farm article.

In order to make a home for your earthworms, you need a medium for them to swim in. There are a couple of choices here. The hardcore gurus use Canadian Peat Moss, which you can get at hardware stores. Peat Moss is lightweight, making it easy for the worms to swim around, but costs money, and has very little food value to the worms. Shredded cardboard, paper, or leaves is popular as well. My favorite is sawdust, or stove pellets.[emphasis added]---Ronnie Ugulano

Another good source of info for raising earthworms.