A review of global trends in the study types used to investigate bee nesting biology

•Species-specific knowledge is a prerequisite for their protection, but for bees, even the relative contribution of different study types remains poorly quantified.•Natural history studies provide most of our fundamental knowledge about bee nesting, with a greater depth and evenness of information across recorded subject areas, except for threats.•Ground-nesting bees and those using natural nest sites are understudied compared to cavity-nesting species or those in artificial nests.