I'm confirming that Red Worms overwintered just fine in bathtub grow beds, left to dry out from Nov. 20, 2011 to Feb. 20, 2012. Around March 5 i spotted live worms. This is an unheated greenhouse. The beds are not insulated. Lava rock in one bed, trap gravel (some kind of igneous, nonpourous rock) in the other.