Nest observations reveal hygienic nest architecture and behavior in an Arctic bumble bee species

Many bumble bee species are declining worldwide. Disease and habitat loss are two contributors to these declines, yet little is known about disease transmission within bumble bee colonies or bumble bee nesting habitat requirements. These gaps are especially wide for Arctic species, as prior bumble bee research focuses disproportionately on the contiguous United States, southern Canada, and Europe. Here, we describe the nesting habitat, spatial distribution, and nest architecture of 10 frigid bumble bee (Bombus frigidus) nests found in the low Arctic in western Alaska. In these nests, we observed a novel nest architecture, the "outhouse," that consisted of an additional subterranean cavity containing concentrated fecal materials and observed that the bees continued to defecate in one or a few locations outside of the main nest cavity when transplanted to the laboratory. Finally, we measured fecal-borne trypanosome parasites in frigid bumble bee workers in this region. Together, our findings provide natural history information on this Arctic bee species and suggest that the outhouse architecture could function as a social immunity trait to reduce the transmission of fecal-borne pathogens within the nest.