In response to spinningayarn.
I have a fairly functional worm farm but am still learning too. I'd leave it till they come to the food before you add more food. See mine in the photo below they've eaten most of their food and are all working on what food is left there. Don't let them dry out and keep something over the top of it all cos they don't seem to like the light, it helps keep them moist too. I use a hessian sack or wet paper/cardboard. I get quite alot of little fruit flys in mine, I think it's because I over feed it a bit but have also read that it might need a very small sprinkling of lime, but haven't got round to it. They prefer mushy food but I give them all sorts. I never give them onion or citrus though as they don't like it. Mine seem to be enjoying a recent layer of shredded paper.
Hope that was some help.