Urban bumble bees are unaffected by the proportion of intensely developed land within urban environments of the industrial Midwestern USA

Urban environments have become an unexpected and promising avenue for pollinator conservation. One group of pollinators, bumble bees, might be especially well suited to utilize the heterogeneous landscape of urban ecosystems. Weedy margins (pervious land adjacent to impervious surfaces such as roads and paved lots) offer plentiful flowers for bees, but are often overlooked in urban pollinator studies. If weedy margins buffer urban bees from loss and fragmentation of foraging habitat in cities, then urban development may not have as strong of a negative effect on bumble bees as previously thought. In this study we test the hypothesis that bumble bee abundance and species richness in these weedy margins will not be affected by the degree of urbanization. We surveyed bees and flowers within weedy plots of land in six industrial cities of the Midwestern USA. Bumble bee abundance and richness were not influenced by the proportion of intensely developed land in the surrounding landscape, but abundance increased with local floral abundance. Bumble bees were also significantly more abundant than other bee groups (honeybees and 'other' wild bees). We found that weedy margins and weedy plant species provide important resources to urban pollinators, and to bumble bees in particular. If small patches of habitat can sustain bees in the city, future efforts of urban pollinator conservation could focus on the installation of high-quality micro-meadows, increasing the availability of quality habitat for pollinators.