Megachilidae > Osmia > Osmia bucephala

Bufflehead mason bee (Osmia bucephala) is a hefty backyard Osmia of late spring. It is one of the largest Osmia in the region, often mistaken for a bumble bee worker. This distinctive box-headed black-and-white mason bee is a frequent resident of suburban yards and gardens, where beard-tongue (Penstemon) flowers are a favorite.

Phenology

One generation per year, active from April through early July.

Range

Widespread, but never very abundant. From Virginia north through Vermont.

Morphology

Size ≈ honey bee 

Females have a very large, dark head (about as wide as its “shoulders”); whitish hairs on thorax and first two segments of abdomen, with the rest of the abdomen black.

Males overall color pattern much like the female, but with more of a metallic sheen to the head and thorax, a white “mustache”, and a long spur on the tibia of the hind leg (which can be obvious in photos).

Similar species

• Bombus impatiens, B. bimaculatus, and B. griseocollis have superficially similar color patterns, but their heads are much smaller relative to the rest of their body and workers carry pollen in corbiculae.
• Anthophora abrupta is similar in color, but has slightly later phenology, black hairs on vertex, narrower cheek, and carries pollen in hind scopal hairs. A. abrupta also often nests in large conspicuous aggregations in the ground.

Nesting

Females nest in cavities, using macerated leaves to create their brood cells. Occurs frequently in at least moderately-disturbed, suburban settings.

Foraging

Generalized, found on a variety of flowers in forests, fields, and gardens. However, seems to have a particular preference for beard-tongues Penstemon spp. and other similar tubular flowers, as well as papilionoid legumes such as vetch (Vicia), indigo (Baptisia), and lupines (Lupinus).

Natural Enemies

No confirmed nest parasites or associates.

Page last updated:
January 17, 2023