Research in Pennsylvania shows that overall colony weight and the number of worker bees to be the leading factors in determining overwintering survival of honey bee (Apis mellifera) colonies. For colonies in which the combined weight of adult bees, brood, and food stores exceeded 30 kilograms, overwinter survival rates were about 94 percent. (Photo credit: Flickr/U.S. Department of Agriculture, Lance Cheung, public domain)