Comparative Evolution of Social and Ecological Traits in Bumble Bees

Bumble bees (<i>Bombus</i>) are prominent keystone pollinators globally and thus serve as model taxa for numerous facets of biology from social evolution to foraging economics. Many of the ∼265 species are in decline, motivating research that aims to better understand which traits make them susceptible. Despite a long history of taxonomic and natural history research, much of their biology is understood from just a few commercially available species. This review compiles the breadth of biotic trait diversity of bumble bees to provide a comparative perspective on their biology, evolution, and conservation. It features ecological traits most pertinent to their conservation, as well as traits of these primitively eusocial bees that inform our understanding of their social evolution. Many of these traits are interdependent, making a broadly comparative analysis valuable for interpreting evolution and declines. These data are organized in a phylogenetic context to show patterns of trait correlation and knowledge gaps, highlighting the depauperate natural history data in Asian and South American species. Limitations in comparative interpretation due to data standardization are emphasized.