Appearance
"Bombus bifarius" has a relatively small body size ranging from 8 to 14 mm for workers and 15–19 mm for queens, with short, even hair covering their bodies. "B. bifarius" individuals express multiple color polymorphisms; however, many similarities exist between these color variants. Hair on the faces of "B. bifarius" individuals is usually yellow or white in color and sometimes exhibits black coloration on the top of the head. In at least the lowermost third of the thorax, there is also black coloration. The hindlegs and pollen baskets can be a brownish-orange or black, depending on whether metasomal tergite 3 is black or not. In the nominate color variant, metasomal tergites 2 and 3 are red, while in the nearcticus color variant, metasomal tergites 2 and 3 are black.
Naming
Its common name refers to the two dominant color polymorphisms, the nominate and nearcticus polymorphisms, present in the species. "B. bifarius" has been identified as one of the two species of bumblebee observed to use pheromones in kin recognition.
Distribution
"Bombus bifarius" is found across mountainous regions of western North America. In the United States, it has been found in parts of Alaska, Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, South Dakota, Utah, Washington, Wyoming. In Canada, it has been found in Alberta, British Columbia, Manitoba, Northwest Territories, Saskatchewan, and Yukon. "B. bifarius" makes its home in various habitats, including open grassy fields, parks, prairies, shrubs, and mountainous areas.
Reproduction
"Bombus bifarius" nests are made underground or on the surface of the ground. These nests are often small and are made up of one singular open chamber. "B. bifarius" can also make their nests in abandoned rodent nests."Bombus bifarius" and "B. frigidus" prefer to mate with non-nestmates, so they have evolved a number of strategies to determine which individuals are kin and which are not. For example, environmental cues like proximity to the nest may indicate that a reproductive female is related. However, not all encounters fall under the category of environmental cues; "B. bifarius" is one of the few bumblebee species that can also determine kin using individually-borne methods. For example, males exhibit a behavior called “patrolling”, in which they mark specific paths with pheromones and “patrol” these paths hoping to encounter a reproductive female that was attracted to the scent. Reproductive females are able to sense these pheromones and are attracted to them.Food
"Bombus bifarius" forages for pollen and nectar from the following plants: Aster, Centaurea, Chrysothamnus, Cirsium, Epilobium, Ericameria, Haplopappus, Helenium, Lupinus, Melilotus, Monardella, Penstemon, Ribes, Senecio, Solidago, and Symphoricarpos.References:
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