Honey bee (Apis mellifera) size determines colony heat transfer when brood covering or distributed

Heat transfer is key to the survival of honey bee colonies (Apis mellifera L.) in the wide range of hot (e.g. sub-Saharan) and cool climates (e.g. maritime-temperate) in which they have evolved and adapted. Here, a validated computational fluid dynamics, conjugate heat transfer model was used to determine the heat transfer of honey bee colonies in simulated standard wooden hives, complete with combs and brood, for a broad range of honey bee sizes, from slender lowland African A.m. scutellata, to broader (larger diameter) Northern European A.m. mellifera, across the whole range of brood covering honey bee densities, as well as when evenly distributed throughout the hive. It shows that under cooling stress, brood covering, broad subspecies need less than a third of the number of bees per unit of brood area for thermal insulation compared to slender subspecies. Also, when distributed evenly around the nest, broad subspecies lose less brood heat than when brood covering. These simulations demonstrate that honey bee girth has climate-based evolutionary advantages directly for the colony as well as via the survival of the individual. In addition, it shows that non-clustering behavioural patterns of passive honey bees can make significant, subspecies distinctive changes to nest heat loss and therefore honey production and climate change survival.