The half black bumble bee (Bombus vagans) is a very common species found throughout Wisconsin and much of North America. It plays an important role as a pollinator in natural and agricultural ecosystems. This medium-sized bee has some distinctive markings that make it easy to identify. Let’s take a closer look at the biology, behavior, and conservation status of this charismatic buzzing insect.
Identification
The half black bumble bee has a primarily black and yellow color pattern. The thorax is yellow with a characteristic small black dot or circle between the wings. The first two abdominal segments are entirely yellow, while the remaining four segments are black.
Queens and workers tend to be a bit smaller than queens and workers of other common Bombus species in the area. Queens have an average body length around 18-22 mm, while workers are 12-16 mm long on average.
Males have similar coloration to queens and workers They can be distinguished by their slightly smaller size, more slender bodies, and a dense yellow beard of hairs on the lower face.
Color Variants
There are some color variants that exist in half black bumble bee populations. Certain males may have extensive yellow coloration on the thorax and abdomen, making them resemble the perplexing bumble bee (Bombus perplexus). Other males may have the yellow on the abdomen reduced to just a narrow band or triangle on the first segment. Queens and workers do not exhibit much color variation.
Nesting Biology
Half black bumble bee queens emerge from hibernation in early spring and begin searching for suitable nest sites. Nests are often made underground in abandoned rodent burrows, dense grass tussocks, or cavities. The queen constructs wax pots out of secreted wax and fills them with a mixture of nectar and pollen to feed the first batch of eggs she lays.
The eggs hatch into larvae that are fed by the queen until they spin cocoons and pupate. After about 4 weeks, the first adult workers emerge. The colony then expands rapidly, with the queen focused on egg-laying while the workers take over foraging and nest care duties.
Colonies typically produce 100-200 workers at their peak by mid to late summer. Reproductive males and new queens are produced by the end of the summer. The colony declines and the old queen, workers, and males all die out, leaving only the young mated queens to hibernate and start the cycle anew the next spring.
Foraging Behavior
Half black bumble bees are generalist foragers that visit a wide variety of flowering plants. Some of their preferred food plants include:
- Milkweeds (Asclepias spp.)
- Beardtongues (Penstemon spp.)
- Asters (Symphyotrichum spp.)
- Clovers (Trifolium spp.)
- Joe-pye weeds (Eutrochium spp.)
- Goldenrods (Solidago spp.)
They are important pollinators of many wildflowers, crops like cranberries and blueberries, and ornamental flowers. Their long tongues allow them to access nectar that other bees cannot.
Foraging takes place during daylight hours when temperatures are above 50°F. Foraging range can extend 0.6 miles or more from the nest. Workers visit 50-1,000 flowers per day and have excellent flower constancy.
Activity Period
Half black bumble bees have an extended colony cycle and long activity period. In Wisconsin, queens emerge from March through May depending on local climate. Colony growth peaks in July and August when large numbers of workers are present.
New reproductive males and queens are produced starting in August. Workers and males die out in late summer and fall, while mated new queens feed heavily to store energy and then find suitable hibernation sites underground.
Distribution and Habitat
The half black bumble bee has a wide distribution across North America. Its range extends from Alaska and Canada south to Georgia and west to California and the Pacific Northwest. It is common and abundant across most of its range.
This species occupies a variety of habitat types, including prairies, meadows, marshes, backyard gardens, agricultural areas, and lightly wooded suburban parks and ravines. It is adaptable and found virtually anywhere there are sufficient flowers to forage on.
Conservation Status
The half black bumble bee has a stable population trend and is not considered at risk currently. It is替 one of the more adaptable Bombus species and seems to be doing well in spite of habitat loss and pesticide threats impacting other declining bumble bees. More long-term monitoring is needed to detect any subtle population changes over time.
This common, widespread species serves as an important pollinator over a long activity period each year. Conserving the half black bumble bee保 helps preserve crucial pollination services for natural ecosystems as well as human food production systems. Providing safe nesting habitat and abundant flower resources through home gardens and urban greenspaces can support its populations into the future.
Fascinating Bees
The half black bumble bee is one of the more recognizable and commonly encountered bees throughout its range. Take time to observe and appreciate this vital pollinator going about its work on flowers in your own backyard. Its unique coloration, long work hours, and role as a keystone species in so many habitats make it a bee worthy of attention, respect, and conservation efforts.
Can be confused with…
Common name: Half-black bumble bee
A common bumble bee found throughout Wisconsin. Queens and workers of this species are typically a bit smaller than average.
Hair medium and a bit shaggy. Thorax yellow, with black circle/dot between wings. Abdominal color standard across castes: the first two segments are entirely yellow, while the remaining four are black. Queens and workers are generally a bit smaller than other common species. Males with similar color patterns, but an obvious yellow beard on the middle of the face. Some male morphs have a mostly yellow abdomen and thorax, which makes them easy to mistake for B. perplexus.
Similar to B. impatiens, long lived colonies. Largest densities possible during July as all three castes are present. Look for new queens in late July and early August.
The half-black bumble bee can be seen throughout Wisconsin. It is likely the third to forth most common species we have.
Seemingly stable, and potentially increasing in abundance. More work is needed to establish a more accurate conservation status for this species.
Half-black bumble bee worker trying to enter nest, filmed by endoscope style camera
FAQ
Do half-black bumble bees sting?
What are the black bumble bees called?
What is a black bug that looks like a bumble bee?
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