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Bombus affinis (rusty-patched bumble bee)



All bumble bees belong to the genus Bombus within the family Apidae. There are approximately 250 described species of bumble bees in the world, and over 50 species in North America (Williams 1998). The family Apidae includes the well-known and economically important honey bees and bumble bees, as well as carpenter bees, cuckoo bees, digger bees, stingless bees, and orchid bees. Bombus affinis (Cresson) was first described by Cresson (1863). Its status as a unique species was recently upheld by Williams (1998) and Cameron et al. (2007).


Bumble bees can be distinguished from other bees by the thick hair covering their head, thorax, and abdomen and the structure on their hind legs called the “pollen basket”. Bombus affinis is known by the common name rusty patched bumble bee, due to a characteristic brownish orange patch on the second abdominal segment of workers and males. Workers are 11 to 16 mm in length, 5 to 9 mm in breadth (Mitchell 1962). Their hair is entirely black on the head, the bottom of the thorax, and in large part on the legs. The rest of the thorax has mostly yellow hair, with black intermixed with yellow near the base of the wings forming a band between the wings with black hairs extending rearward in a narrow V. Their hair is mostly yellow on the first two abdominal segments and black on the rest of the abdomen. The second abdominal segment has a rusty reddish patch centrally, with yellow hairs around the edges of the segment. Bombus affinis queens and workers differ slightly in coloration (an uncommon feature in bumble bees), the primary differences being the absence of the black band and narrow V on the thorax, and the absence of the rusty patch in the in the queen. Queens are 21 to 22 mm in length, 9.5 to 11 mm in breadth (Mitchell 1962), with a black area in the middle of the thorax and entirely yellow on the first two abdominal segments and black on the rest of the abdomen.

Nest Structure

Bombus affinis primarily nests underground, typically in abandoned rodent nests located from six to eighteen inches below the surface (Plath 1927; Thorp et al. 1983; Laverty and Harder 1988). Occasionally nests will be constructed on the surface in areas such as clumps of grass on the ground (Hobbs 1968; Macfarlane et al. 1994).

Activity Period

Bombus affinis are typically active in MN from mid-May through late October, but have been seen from early April to early November.

Commonly Used Flower

Bombus affinis is a generalist, visiting many flowers, but here are a few that are commonly used. Agastache foeniculum, Dalea purpurea, Monarda fistulosa, Penstemon, Solidago

Conservation Status

Bombus affinis is listed as endangered with the U.S. Fish and Wildlife Service. Populations have declined severely since the late 1990s. Bombus affinis is now absent from most of its historic range, but is still found in Minnesota, though at much lower abundances than in the past. More info here: USFWS rusty patched bumble bee


Cameron, S. A., H. M. Hines, and P. H. Williams. 2007. A comprehensive phylogeny of the bumble bees (Bombus). Biological Journal of the Linnean Society 91: 161-188.

Hobbs, G.A. 1968. Ecology of species of Bombus Latr. (Hymenoptera: Apidae) in southern Alberta. VI. Subgenus Bombus, Canadian Entomologist 100: 156-164.

Laverty, T. and L. D. Harder. 1988. The bumble bees of eastern Canada. Canadian Entomologist 120: 965-987.

Plath, O. E. 1927. Notes on the nesting habits of some of the less common New England bumblebees. Psyche 34: 122-128.

Macfarlane, R. P., K. D. Patten, L. A. Royce, B. K. W. Wyatt, and D. F. Mayer. 1994. Management potential of sixteen North American bumble bee species. Melanderia 50: 1- 12.

Mitchell, T. B. 1962. Bees of the Eastern United States. Vol. II. North Carolina Agricultural Experiment Station Technical Bulletin 152: 1-557.

Thorp, R. W., D. S Horning and L. L. Dunning. 1983. Bumble bees and cuckoo bumble bees of California (Hymenoptera: Apidae). Bulletin of the California Insect Survey 23: viii.

Williams, P. H. 1998. An annotated checklist of bumble bees with an analysis of patterns of description (Hymenoptera: Apidae, Bombini). Bulletin of the Natural History Museum, London (Ent.) 67: 79-152. updated at:

Minnesota Record Map

These data are from the Minnesota Bee Atlas project.