Bombus muscorum (Linnaeus,1758)

One of four brown bumblebees known from the British Isles; two of which, B. muscorum and B. humilis, are declining greatly and were  included in research undertaken by the Bumblebee Working Group. The biology of these two species is very similar. Both are associated with extensive areas of tall, but open, flower-rich grasslands, especially those which have many flowers with long corollae, such as clovers, dead-nettles and yellow-rattle. B. muscorum is the more northerly distributed species and tends to occupy damper habitats in the south of the British Isles: however, both species fly together in several areas. Identification is very difficult in the field. In females this relies, in the main, on the presence (B. humilis) or absence (B. muscorum) of black hairs on the thorax in most specimens, although this distinction is not complete. Under a microscope, the form of the pits from which certain of the tergal hairs arise is the best character. The form of the male genitalia is diagnostic but requires microscopic examination. Both species are readily confused with specimens of the much more common B. pascuorum where the black hairs on the side of the abdomen are very reduced. This is a particular problem towards the north. There are a number of distinct forms associated with some of the larger off-shore islands.