Despite the long intertwined evolutionary histories of bees and plants, bee diversity peaks in the xeric areas of the eastern and western hemispheres and not the tropics, where plant diversity is greatest. Intensive sampling in the northeast Chihuahuan Desert of Mexico and the United States provides the first quantitative estimate of bee species richness where high diversity had been predicted in North America from museum records. We find that the density of bee species in a limited area of 16 km2 far exceeds any other site in the world and amounts to approximately 14% of the bee species described from the United States. Long-term studies of bees and other pollinators from areas that are minimally impacted by humans provide much-needed baseline data for studies of bees where human impacts are more severe and as climate change accelerates.
