Fantastic bees and where to find them: locating the cryptic overwintering queens of a western bumble bee

Bumble bees are among the best‐studied bee groups worldwide, yet surprisingly we know almost nothing about their overwintering habitats nor the microsite characteristics that govern selection of these sites. This gap represents a critical barrier for their conservation, especially if preferred overwintering habitats differ from foraging and nesting habitats. Current conservation plans focus on foraging habitat, potentially creating a problem of partial habitats where improved forage might fail to prevent population declines due to limited overwintering sites. We provide the first data on the overwintering habitat for any western North American bumble bee. Our data suggest that overwintering and foraging habitats are likely distinct, and queens’ selection of overwintering sites may be shaped by environmental stressors of the year. In our study area, queens overwintered in litter beneath cypress trees, where no floral resources exist. Whether this separation of overwintering and foraging habitat holds for other bumble bee species remains to be discovered. Our data highlight the need to consider the whole life cycle for understanding population dynamics and conservation planning. This need is underscored by growing evidence for the decline of multiple North American bumble bee species. Bumble bees are among the best‐studied bee taxa worldwide, yet certain stages of their annual social life cycle remain unknown for nearly all species. In spring, a mated queen emerges from her overwintering site, searches for a spot to nest, and works alone to raise a first cohort of worker daughters. The colony grows over several months, producing successive cohorts of workers before switching to produce males and new queens. In mid‐ to late summer, newly mated queens seek sheltered sites where they overwinter. We know a great deal about bumble bee foraging and some about nest‐searching queens and nest establishment in spring (Kells and Goulson 2003, Suzuki et al. 2009, Lye et al. 2012, O'Connor et al. 2017). We know almost nothing about overwintering queens (Alford 1969, Liczner and Colla 2019). Overwintering sites have been described for only a handful of species (Sladen 1912, Plath 1927, Alford 1969), and hibernating biology is poorly understood even in commercially raised species (but see Hobbs 1967). This knowledge gap is alarming, given bumble bees’ importance as pollinators and well‐documented declines of species from multiple geographic regions (Williams and Osborne 2009, Cameron et al. 2011). Our understanding of bumble bee habitat needs is primarily shaped by