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Abstract 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.

Abstract Fire is a dominant, and well‐studied, structuring force in many temperate and semi‐arid communities; yet, few studies have investigated the effects of fire on multi‐trophic interactions. Here, we ask how fire‐induced changes in flowering affect the abundance of bumble bee foragers (Bombus vosnesenskii) and whether differences in floral resource availability are due to changes in plant species composition or lengthened bloom of a consistent set of species within burned and unburned grasslands. Following fire, burned and unburned sites had similar early spring bee and floral abundances. However, after the early bloom, forager activity remained high only in burned sites, where floral abundance persisted for longer. Importantly, the increased floral abundance following fire was due to a lengthening of within‐species flowering phenology, as burned areas later in the season retained floral abundance and composition similar to that of unburned areas early in the season. Furthermore, density of flower patches chosen by bumble bee foragers was significantly higher at burned sites, suggesting an increase in patch quality for foragers in post‐fire communities. Our results suggest positive effects of fire for bumble bee foragers and forb communities in California grassland ecosystems in the year following disturbance, namely through differences in plant phenology and floral density. We conclude that fire‐induced changes in flowering phenology can alter interspecific interactions and benefit pollinators.