I put my old cultures in the garage till I get the time to put them in rubbish, this week it is near 0 degrees here, and I had a culture ..ok 50 cultures in garage and when going to dump them I noticed one had hydei flies all over inside one container, the garage was at 50 or so at the time, I open the door so the woodburner heat goes in there when I have to work in it, thats how they were movin around, so from the 3 or 4 times I have frozen them, I believe they do COME BACK!