Horn-faced mason bee (Osmia cornifrons) and Taurus mason bee (Osmia taurus) are two similar nonnative Osmia. Both have spread rapidly throughout eastern North America in recent decades since their introduction as potential fruit tree pollinators in the 1980s. These species have proliferated in human-altered habitats, raising concerns over potential impacts on native Osmia spp., which O. cornifrons and O. taurus may compete with for nesting cavities. Any large, brownish, hairy mason bee encountered in urban areas or suburbs in early spring is a member of this species pair.
Early spring. Active March through June, with one generation per year.
Widespread. Along coasts from Virginia to Massachusetts, and north inland to Burlington, Vermont and Toronto, Ontario.
Size ≈ honey bee
Females: medium-large Osmia, covered in long, pale brownish hair; face with two distinctive pointed projections (“horns”)
Males: much like females, but with very noticeably longer antennae and without horn-like projections on the face.
- These two species are the only obviously brown Osmia in the region.
- O. cornifrons and O. taurus and hard to differentiate in the field. O. taurus tends to have hair that is more orange in color (vs. plainer brown/tan in cornifrons). Facial projections of O. taurus females are shorter than the long “horns” seen in O. cornifrons, but these facial projections are hard to see without close photographs.
Solitary, cavity nesting. Not especially picky about choice of nesting location, using holes in a range of structures from building walls to dead snags.
Generalist, visits many plant taxa including early-blooming nonnative shrubs (e.g., Pieris, Lonicera).
None known in North America.
Page last updated:
January 17, 2023