Honey bees actively process dead mice inside their nests

Abstract Honey bee nests are warm and resource-rich, making them attractive targets for animal intruders during winter, including mice. Beekeepers often protect their nests from mice, but have also documented mouse skeletons coated in propolis, an antimicrobial mix of plant resins and beeswax. While the start (mouse intruder) and end (mouse “mummy”) are reported, the progression between the two has not been observed and documented. Using modified observation hives, we tracked four colonies as they processed dead mice, quantifying carcass decay and accompanying worker behaviors. Colonies processed carcasses without assistance from other animals (e.g., necrophages). Workers actively broke carcasses down by chewing and tugging at tissue, dismembering and ejecting portions of the mouse, and even sucking putrefactive fluids. These behavioral patterns were consistent across colonies. No replicate, however, yielded a carcass coated in propolis, and we only detected one worker applying propolis in 144 hours of observation. A second experiment, adding 20 carcasses to traditional nest boxes during winter, resulted in 6 of 9 winter-surviving colonies ejecting their mice and 6 of 11 colonies dismembering and/or ejecting their mice before dying during winter. This suggests that a colony’s primary goal is to remove the carcass entirely, including via ingestion of decomposition fluids, and that reported cases of propolized skeletons are likely due to texture rather than microbial risk alone. This study is the first to describe how honey bee colonies process vertebrate carcasses in their nests and highlights the active role workers take in processing and removing foreign bodies.