I had three large worm beds as a kid in Northern California. I sold worms to the local sporting goods store. Freezing temperatures started in mid to late September and continued on and off into early May. Every once and while we would get down around 18 degrees for a few days during winter. A week or so of snow on top of the beds did not seem to both them. Before freezing weather we would clean the rabbit hutches and put everything on top of the worm beds. This fed the worms and insulated them. We also put spent plant material on the worm bed, normally tomato vines and bean plants, and others.
This created high nutrition worm beds. I think the waste from the rabbits super charged the worm beds. The worms produced in the beds were large then those normally found in the stores.