Western Bumble Bee

Pronunciation

How to pronounce Bombus occidentalis: /ˈbɒmbəs ˌɒksɪˈdɛntælɪs/

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Summary

Bombus occidentalis, or Western Bumblebee, once common in Northwestern America, has experienced significant population declines, particularly in the Pacific states. It exhibits various color forms depending on geographic location and plays a vital role as a pollinator.

Physical Characteristics

Western bumblebee workers have three main color variations: 1) Northern California to British Columbia: yellow hair on thorax, black hair on fourth abdominal segment, whitish lower edge of fourth and fifth segments; 2) Central Coast California: yellow hair on second and third segments, reddish-brown hair on fifth segment; 3) Rocky Mountains to Alaska: yellow hair on thorax behind wings and on second and third abdominal segments. Drones have seven abdominal segments, while females have six. Drones' antennae have 13 segments, females have 12.

Identification Tips

Identification based on coloration of abdominal segments, which are numbered T1 to T6. Workers have distinct color patterns, and males can be distinguished by their additional abdominal segment and lack of stingers.

Habitat

Nests underground in cavities or burrows, often those left behind by rodents or other animals.

Distribution

Found from the Mediterranean California to the Tundra regions of Alaska, but has seen a notable decline in population, especially in California, western Oregon, and western Washington.

Diet

Generalist foragers feeding on nectar and pollen. They collect nectar for carbohydrates and pollen for protein.

Life Cycle

Colony begins with a solitary queen who lays eggs and raises the first brood of female workers. The colony can expand to around 1,600 workers, and persists from early spring until late November. The old queen and workers die in winter, leaving gynes to hibernate.

Reproduction

Colony reproduction involves one queen that lays eggs; new queens (gynes) hibernate to start new colonies in spring.

Predators

May include other insects such as predatory wasps and natural animal predators.

Conservation Status

Vulnerable (IUCN Red List). Decline noted in the Pacific states, particularly California.

Ecosystem Role

Pollinators, aiding in the fertilization of many flowering plants, contributing to ecological health.

Economic Impact

Commercially reared for crop pollination; historically important for crops like tomatoes, avocados, and blueberries.

Health Concerns

Susceptible to diseases transmitted through commercial bumblebee rearing, such as Nosema, with implications on wild populations.

Evolution

Distinct species confirmed through DNA evidence, with potential subspecies based on geographical populations and haplotype differences.

Similar Taxa

• Bombus terricola
• Bombus impatiens

Misconceptions

Often confused with closely related bumblebee species such as Bombus terricola.

Tags

• insect
• bumblebee
• pollinator
• conservation
• endangered