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Endangered Species Program
Conserving and restoring threatened and endangered species and their ecosystems
Rusty Patched Bumble Bee
Life History - - Excerpted from the Species Status Assessment
Bombus affinis is a eusocial (highly social) organism forming colonies consisting of a single queen, female workers, and males. Colony sizes of B. affinis are considered large compared to other bumble bees, and healthy colonies may consist of up to 1000 individual workers in a season (Macfarlane et al. 1994, pp. 3-4). Queens and workers differ slightly in size and coloration; queens are larger than workers (Plath 1922, p. 192, Mitchell 1962, p. 518). All B. affinis have entirely black heads, but only workers and males have a rusty reddish patch centrally located on the abdomen.
Bombus affinis annual cycle begins in early spring with colony initiation by solitary queens and progresses with the production of workers throughout the summer and ending with the production of reproductives, males and new queens, in mid to late summer and early fall (Macfarlane et al. 1994, p.4; Colla and Dumesh 2010, p. 45; Plath 1922, p. 192). The males and new queens disperse to mate and the original founding queen, males, and workers die. The new queens go into diapause (a form of hibernation) over winter. The following spring, the queen, or foundress, searches for suitable nest sites and collects nectar and pollen from flowers to support the production of her eggs, which are fertilized by sperm she has stored since mating the previous fall. She is solely responsible for establishing the colony. As the workers hatch and the colony grows, they assume the responsibility of food collection, colony defense, and care of the young, while the foundress remains within the nest and continues to lays eggs. During later stages of colony development, in mid-July or August to September, the new queens and males hatch from eggs. At the end of the season the foundress dies and the new queens (gynes, or reproductive females) mate before hibernating.
Bombus affinis has been observed and collected in a variety of habitats, including prairies, woodlands, marshes, agricultural landscapes, and residential parks and gardens (Colla and Packer 2008, p. 1381; Colla and Dumesh 2010, p. 46 ; USFWS RPBB unpublished geodatabase 2016). Bombus affinis requires areas that support sufficient food (nectar and pollen from diverse and abundant flowers), undisturbed nesting sites in proximity to floral resources, and overwintering sites for hibernating queens (Goulson et al. 2015, p. 2; Potts et al. 2010, p. 349).
Bumble bees are generalist foragers, meaning they gather pollen and nectar from a wide variety of flowering plants (Xerces 2013, pp. 27-28). Bombus affinis is a short-tongued species (Medler 1962, p. 214), so they are not able to easily access the nectar in flowers with deep corollas (all of the petals of a flower). The species is one of the first to emerge early in the spring and the last to go into hibernation, so to meet its nutritional needs, B. affinis requires a constant and diverse supply of flowers that bloom throughout the colony’s long life cycle, from April through September (MacFarlane et al. 1994, p. 5). The nectar from flowers provides carbohydrates and the pollen provides B. affinis with protein. The number of queens that a colony can produce is directly related to the amount of pollen that is available (Burns 2004, p. 150). It has been suggested that B. affinis needs floral resources in close proximity to its nest sites, because studies of other Bombus species typically exhibit foraging distances of less than 1 km from their nesting sites (Knight et al. 2005, p. 1816; Wolf and Moritz 2008, p. 422; Dramstad 1996, pp. 163-182; Osborne et al. 1999, pp. 524-526; Rao and Strange 2012, pp. 909-911). Bombus affinis may also be dependent on woodland spring ephemeral flowers because of the species’ early emergence in the spring and is often associated near woodland habitats (Colla and Dumesh 2010, p. 45-46). The availability of floral resources is dependent on the proper soil and precipitation conditions to sustain them. Extended periods of drought, for instance, may lessen the availability and diversity of flowering plants in a given area because plant phenology is primarily driven by temperature, precipitation, and the timing of snowmelt in the spring (Inouye and Wielgolaski 2003, p. 207; Wielgolaski and Inouye 2003, pp. 179-181; Pyke et al. 2016, p. 12).
Bombus affinis nests are typically in abandoned rodent nests or other similar cavities, one to four feet below ground (Plath 1922, pp. 190-191; Macfarlane et al. 1994, p. 4). Bombus affinis nests have also been occasionally observed above ground (Plath 1922, p. 190). Little is known about the overwintering habitats of B. affinis foundress queens, but other species of Bombus typically form a chamber in soft soil, a few centimeters deep and sometimes use compost or mole hills to overwinter (Goulson 2010, p. 11).
Bombus affinis live in temperate climates, and are not likely to sustain prolonged periods of high temperatures (over 35° Celsius (C) (95° Fahrenheit (F)) (Goulson, pers. comm. 2016). Bombus are able to fly in cool temperatures and low light levels, particularly in comparison to other bees, which can extend their daytime foraging times (Corbet et al. 1993, p. 20). Table 2.1 summarizes ecological requirements at the individual level.
Table 2.1. The ecological requisites for survival and reproductive success of B. affinis individuals.
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Last updated: March 12, 2018