Sounds like the bed heated up and they left. If conditions are right they will stay and thrive in that bed. May also have dried out to much mabye.

2 lb of worms is not very many worms for such a large space.
I have a 2' by 4' bin and when I got my 2# of worms the seller recomended that I divide the bin in half and start out only using one side (2' by 2') so the worms would stay close enough together to find eachother to mate. It is now several months later and the first half of the bin looks like it is getting close to being ready to harvest castings so I put bedding in the other half and started feeding over there. There are still plenty of worms and eggs in the first half so I will wait quite some time before harvesting castings.

Anyway, as to if your compost is ready to use, that is probably largely up to you. If it smells good and looks good to you, you could probably use it. Stuff like shredded leaves and composted manure are usually fine for used in the garden as they were.

As to your worm population, if you wanted you 4' by 8' bed to be teeming with worms, you probably would have needed to start with about 16 lbs of worms. 2 lb of worms spread out over such a space probably had trouble finding each other to mate when the temperatures were right. Worms can breed fast but that usually only happens when all conditions are right, good bedding, right temperature range, abundant food, and another worm their size to mate with. With patients your worm population may rebound, just keep the regular additions of food and leaf litter happening. Perhaps if you keep your feedings to once section of the bed the worms will congregate to that area more and breed for you. Also a sprinkling of cornmeal is supposed to be a real treat for them.

Good luck

Thanks for all the good ideas. I'll try dividing the bed this time around as I'm about to try it again with leaf litter, horse manure and added kitchen scraps this time. And a bit of cornmeal for a treat. I was also thinking about adding peat moss as I need to give them enough food to hold them over all winter and I've read not to disturb the bed once it's covered up against the cold.
More questions though... is horse manure ever too old to use and how would I know? The stuff I have is not right out of the stables and has been piled in the field. Lots of hay mixed in with no odor at all. I understand you don't want it too fresh in case the horses have been recently de-wormed. Also I always wonder about the amount of water to add. I've heard the thing about the wet sponge, but it's difficult to judge. 16 lbs of worms seems like a lot and expensive, too. Maybe 4 lbs for a 4 by 4 bed? Thanks in advance.

thymesup,
You need a good volume of mulch and protection to keep you worms warm for the winter so perhaps instead of making a small worm bin you might do something like a bin within a bin.
What I am thinking is section off a bit of the center of your existing bin and collect as many of your worms there as you can in some bedding material (shredded leaves and cardboard would probably be great.) To section that area off from the rest of the bin you could do something as simple as a cardboard box. 2' by 2' for 2 # of worms or perhaps 2' by 4' for 4 # of worms. I'm not really an expert so these are just guesses on my part.

Anyway the cardboard box of worms in the middle will decompose and they can escape if they need but hopefully it will keep enough of them close enough together for a while that they can breed and keep your population going. Anyway, that center box should have their favorite bedding and foods . Then in the rest of your 4' by 8' bed you can fill with your other compost materials which should help keep the worm bin a good temperature over the winter as well as providing food if your worms eat their way out of the box (they love cardboard by the way as the glue provides some protiens and the corrigations invite them to crawl in and be cozy.) Perhaps you might line the entire big bin with cardboard if you have a easy free supply of the stuff. Anyway, you don't really want to get a hot compost going (hot would cook the worms) so old horse manure, leaves, perhaps a small amount of nitrogen material like used coffee grounds spread around the rest of the bin. Make sure everything is moist and cover over with more dampened cardboard and your plywood lid. This is just an idea.

Your worms may spread out if the conditions in the center box are not to their liking but perhaps you will have another generation that will hatch and keep things going. You may also have a wonderful usable batch of compost from the horse manure and leaves that you can spread around the garden along with worm castings.

I have the opposite problem from you, I'm not worried about my worms freezing in winter but cooking in summer, I put frozen bottles into my bin in summer.

I now have several large (20 ftx5 ftx 2 ft) beds that were started with just a few (well under half a pound) worms each. I fill the beds with raw materials (weeds, kitchen scraps, paper, cardboard, etc.), dump the worms in, and go to it. My mix of raw materials is so high in carbon that I don't get excessive heating. I don't bother with shreding any of the materials any more; I found that the larger materials broke down fast enough without shreding, and shreding is just more work for me. My experience is that the worms breed quite readily in these large bins, even if you start with just a few worms; they find each other fine, and enjoy the wide variety of materials available as they rot. I eventually use these beds for planting crops in them. Many plants love to grow in the mature beds. I continue to add a supply of compostable materials to keep the bed levels high enough. I've done this both outside, in a zone 4-5 climate, and inside in a greenhouse. My experience outside is that if you just load up the bed with materials in the fall, that the worms will find a comfortable, above freezing location, and be fine over the winter. I believe that your setup would provide quite suitable winter protection. I found that I could add materials to the top all winter without problem. As the top-added materials got covered, they rotted, provided some heat and protection, and new food for the worms. In summary, I'd suggest not worrying too much about the setup you have; try dumping lots of material in, using the worms you have, and see what comes out in the spring. By the way, one of my most active bins, which I have had going for about four years now, probably has hundreds of thousands of worms now. I periodically give friends about 15 gallons of the bedding and worms to start their own bins; there are thousands of worms in these 15 gallon containers, but they are quickly replaced in the big bins I have. Hope this helps.
Renais

Renais, sounds like you've got a great thing going there. Thanks to everyone for your responses.
Still wondering why I have so few worms. They obviously lived long enough to process the material in the bin last fall. Should I have added new food sooner in the spring? Was the bin too dry? I did not add water all winter. I doubt that the bin got too hot, as I added very little green and the bin is in the shade in the summer.
Renais, when you are working your bins how often do you wet down the bedding? Thanks.