I would ask you a few questions:

1. How big is your bin and how many worms do you have?

2. What kind of worm do you have?

3. What (and how often) do you feed them?

I don't have a lot of worms (red wigglers) I split my bin up with my brother after a few months when I started it with 2000 worms. I would guess there are probably 500 in my bin right now. We had a very bad ice storm here in southern Indiana at the end of January and we were without power for 7 days. The room the worms were in probably got down below freezing during that time. Over the winter months I probably only fed them once a month but I usually feed them every couple weeks from very "ripe" kitchen waste. I haven't checked down into the bin to see how they are doing, but the food is mostly gone each time I feed them and they have plenty of moist bedding. The worms I do see on top when I move the bedding to feed them are looking very healthy and seem to be doing well now. I'm wondering if the ice storm got to them... I never even thought of them during that mess trying to keep our other pets and family members warm.