I would think putting in a good layer of mulch would help with survival of the worms in your raised bed. See a related thread on this topic at the link below.

Here is a link that might be useful: Related chat on GW Vermicomposting Forum

i have been gardening this method for several years. so there has always been mulch and worms have servived. Recently when digging in the garden I see sluggish worms. i want them being more productive.

I have tried and currently am trying what you are talking about with mixed results. There just is not enough mass to create and hold enough heat. My worms slow down and retreat lower during the cold months, but thrive when it warms up in the spring. The "lasagna style" beds with horse manure, UCG ect and straw mulch stay a few degrees warmer, but not warm enough!. I have had success in the winter creating heat with larger piles. Worms populate them and stay very active.

I checked today and soil temp was 40F and the lasagna bed was 45F.
I have a compost cage I seeded with bedrun worms and have slowly built up over the last 3 months. It is 2' deep x 3' wide and measured 70F.
Another recently built pile is 120F.
My larger windrow has cooled to 45-50F and the squirm is quite inactive.
Love my new compost thermometer.

"keeping worms warm in winter months"

"I live in Ga. just south of Tn."

What? For the winter months mine take a plane to North Carolina and catch some rays for that vitamin D. I am so confused.

~ Connecticut

thanks mendopete.. that was exactly what I wanted to know and especially helpful that you knew the temperatures.

"For the winter months mine take a plane to North Carolina and catch some rays for that vitamin D."

I'm not at ALL confused...I want to go with them, have they left yet?

Just north of Boston, on the coast!