|scientific name Bombus terricola |
Areas with dense vegetation, nests are underground with downward sloping entrances (Hobbs 1968).
Among the earliest bumblebees to emerge and establish nests in spring (Hobbs 1968).
Females of the subgenus Bombus s. str. can be distinguished by ocelli on the superorbital line, and flagellomere one being equal in length to flagellomere three. Bombus s.str. males can be distinguished by non-protuberant compound eyes, short antennae, and penis valves that form a wide vertical plate (Thorp et al. 1983). Bombus terricola have abdominal segments 1 and 4-6 covered with black pile while segments 2-3 are covered with yellow pile; the malar space is one-fifth to one-sixth the length of the eye(Franklin 1912). Bombus terricola can be distinguished from its close ally Bombus occidentalis nigroscutatus by the presence of yellow pile on the second abdominal segment (Franklin 1912).
Franklin (1912) describes the queen as varying in length from 15 mm to 18 mm; in wing spread from 37 mm to 40 mm; and in width of second abdominal segment from 10 mm to 10.5 mm. Workers range in length from 10 mm to 14 mm; in wing spread from 26 mm to 33 mm; and in width of second abdominal segment from 5 mm to 8 mm. The length of males varies from 11 mm to 15 mm; wing spread from 27 mm to 33 mm; and the width of second abdominal segment from 6.5 mm to 8 mm.
Alford (1975) outlines the life history of Bombus terricola. Newly mated B. terricola queens overwinter beneath the soil litter and emerge from their hibernacula in late spring. Queens are transitory for a time, growing in size while collecting pollen and looking for a suitable nest. Once a suitable nest has been found, the queen constructs an apple sized hollow structure within it. The queen deposits her eggs within a mound of pollen on the floor of the structure; she also constructs a honeypot for storing nectar. Newly hatched larvae begin consuming the pollen mound, requiring the queen to continue provisioning it. The queen periodically incubates her brood by sitting upon it and respiring to generate body heat. The larvae spin cocoons in the final instars, as do the pupa; the cocoons may be re-used later for storage of pollen or nectar. Upon pupation, the emerged adults take nectar from the honey pot. Once the nest consists of the new young workers and the queen it can be considered a social unit and is referred to as a colony. Subsequent generations are produced differently from the first: new eggs are laid in clumps in cells atop the pupating first generation of workers, and workers are now responsible for provisioning of the growing larva and the honey pot. The caste differentiation of each generation varies throughout the year, with the first generations containing all workers, followed by a worker/male split, followed by mostly males, followed by a male/queen split, followed by mostly queens. The factor initiating queen production has not been established but it appears the colony must reach a size capable of maintaining nest temperatures and food stores before queens are produced. Young queens remain in the colony and will mate during their first week. Males leave the hive and do not return; they establish a methodical flight path and mate with encountered queens. Only the newly mated queens will overwinter in hibernacula; males, founder queens, and all workers perish.
Of concern, populations rapidly declining (Colla and Packer 2008, Grixti et al. 2009).
Have been observed foraging upon milkweed and dogbane species of the family Apocynaceae (Plowright and Plowright 1998).
Eastern nearctic region (Williams 1998).
There are reports of colonies being usurped by Bombus affinis (Alford 1975). Hobbs (1968) reports parasitism of a B. terricola nest by Bombus insularis and Bombus suckleyi.
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