We've got great resources on our site and on YouTube for keeping your worm bin warm over the winter, ranging from using natural techniques to getting some manmade help!
Steve's #1 recommendation is to use the seed starting mat linked below.
Blog Article on Winter Vermicomposting
https://urbanwormcompany.com/winter-vermicomposting-how-to-keep-a-worm-bin-when-its-cold/
YouTube Video on Winter Vermicomposting
https://www.youtube.com/watch?v=ZQYkDBvZw0c
Recorded Livestream on Cold Climate Vermicomposting
https://www.youtube.com/watch?v=W06_GhrbIiU
Video on Using Seed Mats to Keep Your Worm Bin Warm
https://www.youtube.com/watch?v=8Uk747936uY
Link to Seed Starting Mat That's Perfect for Winter Vermicomposting