Osmia lignaria

Taxonomy

Osmia lignaria is in the subgenus Osmia within the Osmia genus. Bees in the genus Osmia, in the family Megachilidae, are known as the mason bees because some of them build their nests from mud. Some members even build free-standing nests. They overwinter as adults and are the first bees active as soon as the snow is mostly melted. Osmia lignaria, also known as the "blue orchard mason bee," is the most common Osmia we found, nesting throughout Minnesota, with more nests in the Eastern Broadleaf Forest and Laurentian Mixed Forest provinces. 

Description

Osmia lignaria, like many Osmia sp., have a metallic blue-green shine to their exoskeletons. You may need to get them in the right light to see this color; otherwise they may look mostly dark. They are a large bee, almost as big as a honey bee, and the males especially have a lot of white or light-colored hair on their heads and thoraxes. The females carry pollen under their abdomens, like all Megachilidae, and their scopal hair is black.

Nest Structure

Osmia lignaria is the only Osmia species in Minnesota that builds their nest walls and plugs from mud (see graph). The outer mud plug is frequently left lumpy in texture, in contrast to some wasps that also use mud but tend to smooth the outer plug.

Hole Sizes

Osmia lignaria most commonly used upper and lower column 2 holes (1/4", 5/16" diameter) in the Bee Atlas blocks. Column 1 holes (3/8", 7/16") were also used quite often, and to a lesser extent, lower column 3 holes(3/16"). See graph below. 

Voltinism

Univoltine, meaning they complete one generation per year in Minnesota. Both males and females overwinter as adults inside their cocoons.

Activity Period

Very early spring. These are the first bees out (usually in early April) and their nests are usually the first plugs we see in any blocks. Bee Atlas volunteer data show that nests may be completed as early as mid April until the middle of June (see graph). In USDA hardiness zone 3, nests may be completed a slightly later than in zone 4.

References

No information at this time.