What do night crawler eat?

I have some night crawlers for science fair. One is supposed to be the control (just water), and the other gets a special diet (food scraps and water). They are in two different pots that are filled with Top Soil Miracle Grow and get about 1.5 liters a day. would the control group die, or would they just have to eat dirt? If they were to die, how could i prevent that WITHOUT giving the control group scraps? Is there some where I could get "worm food"?