Invertebrate Red Book of Spain. Pdf concerning Bombus species listed in the Red Book of Invertebrates of Spain.
Natural History Museum (London): Page with a large number of scientific publications on bumblebees by Paul Williams. It also has identification keys to colour patterns in bumblebees and keys of male genitalia.
IUCN (International Union for Conservation of Nature): List of species evaluated by the IUCN. This page show international conservation status and threats of some species of Bombus.
Smithsonian Tropical Research Institute (Panama). Bombus phylogeny by Kawakita et al.
Web pages with images of Bombus.