6 spp. (of which 2 non-native) in our area, 12 spp. total(1)
Head and malar space short. Midleg with rounded angle.
A holarctic group; in our area B. terricola
is widespread in Canada and the northeastern USA, B. occidentalis
is in western Canada and the western half of the USA, B. franklini
has a very narrow historic range in southern Oregon and northern California (with no records since 2006), and B. affinis
occurs in the e. half of the US and adjacent southeastern Canada; B. cryptarum
is found in Alaska and western Canada(1)
Forest-edge, mountain meadow, and grassland(2)
Nests underground; colonies can be large(2)
Abrupt and severe declines of bumble bee species in this subgenus were widely reported soon after development of the commercial bumble bee industry and detection of high rates of parasitism in managed colonies. These abrupt losses occurred in the absence of any apparent loss or modification of habitats and are unlikely to be due to pesticides as other bumble bee species, e.g. members of subgenus Pyrobombus, remain abundant at the same sites.
Of greatest concern is loss of Bombus franklini, narrowly endemic to southern Oregon and northern California and not seen since 2006 despite resurveys by bombus specialist Robbin Thorp. Loss of B. affinis from much of its range, in eastern North America, is also very troubling.
A neglected aspect of these declines is loss of the cuckoo bumble bees B. ashtoni and B. suckleyi. These depend on Bombus (Bombus) as hosts and have also severely declined as evidenced by lack of any photos of live individuals on Bugguide.
Recent attention given to local pathogen spillover from particular greenhouses has diverted attention away from the possibility of a broad-scale epizootic.