The rusty patched bumble bee is extremely rare in Wisconsin and is considered both state- and globally-imperiled. In 2017, The U.S. Fish and Wildlife Service listed the rusty patched as endangered under the Endangered Species Act. Once considered common in the northeastern U.S. and the upper Midwest, recent observation records are mostly from the upper Midwest and are of single individuals. In Wisconsin, recent observations are mostly from the southern half of the state.
The Ashton cuckoo bumble bee (Bombus bohemicus) is a nest parasite of rusty patched bumble bee (Williams et al. 2014). The Ashton cuckoo has not been reported in Wisconsin since 1979.
The rusty patched, like other bumble bees, live in colonies composed of a single queen and female workers. Colonies start to produce new queens and males in the mid- to late summer. Only new, mated queens overwinter, emerging from diapause (a form of hibernation) in the spring. New queens are responsible for finding a new nest site, laying eggs, and for all of the foraging and care of the colony until the first workers emerge (Hatfield et al. 2015). Once the first workers emerge, the queen remains in the colony laying eggs. Bumble bees need areas that provide nectar and pollen from flowers throughout the duration of the colony life cycle, and suitable sites for nesting and for overwintering queens.
Worker – Face and vertex black. Thorax mostly yellow with a black spot or band between the wingpads often triangular-shaped pointed away from the head. Abdominal segments T1-2 yellow with a brown or rusty patch on T2 towards the center surrounded by yellow; T3-6 black.
Queen/gyne – Similar to workers except they are completely yellow on T1-2 and do not have a "rusty" patch. Queens/gynes are larger than workers and appear earlier in the season.
Male – Similar to workers except males have light hairs on the vertex.
Other distinguishing features – Short face and medium length hair. Queens/gynes have short even hair.
Counties with verified B3 observations (in green).
Description of Habitat/Range:
Known habitats include prairies, woodlands, marshes/wetlands, agricultural landscapes and residential parks and gardens (Williams et al. 2014). Overwintering habitats include loose and often sandy soils or woodlands. Nest sites have occasionally been found above ground in clumps of grasses, but are usually 1-4 feet underground in abandoned rodent nests or other cavities (USFWS 2011).
The rusty patched bumble bee is a short-tongued species (Williams et al. 2014), typically found on open flowers. Nectar plants include Aesculus (buckeye), Agastache (hyssops), Asters, Helianthus (sunflowers), Lonicera (honeysuckles), Monarda (bee balms), Physotegia (obedient plant), Prunus (plums/cherries), Solidago (goldenrods), and Vaccinium (blueberry) (Williams et al. 2014, Colla et al. 2011, Watson pers. com).
The rusty patched emerges early in spring and is one of the last species to go into diapause. In Wisconsin, observations have been reported between April and October.
Colla, S., Richardson, L. and Williams, P. (2011) Bumble Bees of the Eastern United States. A product of the USDA Forest Service and the Pollinator Partnership with funding from the National Fish and Wildlife Foundation.
Hatfield, R., Jepsen, S., Thorp, R., Richardson, L., Colla, S., Foltz Jordan, S. and Evans, E. (2015) Bombus affinis. The IUCN Red List of Threatened Species 2015: e.T44937399A46440196.