???My compost heap has at least 3 different types of bumble bee nesting in it. I know that they will die out over winter and only the queens live to start a new colony next year. My question is - when is it safe to use my much desired compost without the risk of disturbing a colony of bees that are still viable? :-\
When the bees disappear. It all depends on the weather in early autumn, and I think on the species of bee as well. But you should be OK after the first frosts.