Osmia is a widespread genus primarily active in the spring from the first warm days of April into June. While many are difficult to ID even with a microscope, there are several larger species that are of conservation concern that can be readily recognized from photos.
Most nest in above ground cavities, including hollow stems. Look for them in shrubby areas and attract them to your yard by leaving dead stems standing. As of January 2021, 15 species in the genus Osmia have been recorded in Vermont, 4 of which have been confirmed through iNaturalist.
Genus level ID
As pollen-collecting members of the family Megachilidae, females have pollen carrying hairs on the underside of the abdomen. These hairs are referred to as scopal hairs, and are either bright white or black depending on the species. Most Osmia are a shiny blue color, though two non-native and a few very rare species have dark bodies. The non-native ones – the Hornfaced Bee and Taurus Mason Bee – are covered with pale orangish hair that make them distinctive as a group.
Most are smaller than a honey bee, though one, the Bufflehead Mason Bee, is large enough to be occasionally mistaken for a bumblebee.
In most species, the females are easier to identify from photos.
Leafcutter Bees (Megachile) – Leafcutter Bees lack the metallic shine of most Mason Bees and many Leafcutters have distinct hair bands on their abdomen. In addition, they are generally larger and active later in the summer (June – October).
Small Mason Bees (Hoplitis) – As the name implies, Small Mason Bees are smaller than most Mason Bees. One rare species, the White-fronted Small-Mason (Hoplitis albifrons) could be confused with a Mason Bee, though it lacks any metallic shine.
Species likely not identifiable from photos
Unless otherwise specified, photos in the grid are courtesy of Margarita Miklasevskaja at PCYU with funding from NSERC-CANPOLIN.
Please note that many of our datasets have not been published yet, so the maps are incomplete.