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Osmia albiventris (Mason bee)
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Taxonomy
Bees in the genus Osmia, in the family Megachilidae, are known as "mason bees" because some species use mud to build their nests. 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 albiventris is one of several smaller Osmia recorded in our state. It was found rarely in the Bee Atlas project, primarily in St. Louis Co., along the shore of Lake Superior.
Description
Osmia albiventris look very similar to Osmia pumila at first glance. Closer inspection would show wider unpitted bands on the top of the abdomen as compared to O. pumila. Osmia albiventris females have light scopal hairs.
Nest Structure
Nest are built and plugged with chewed vegetation material. Although one Bee Atlas nest had a partial mud plug recorded for its final plug, the other Bee Atlas nests were made with chewed vegetation, which corresponds to information from 3 nests in Medler (1967). Bees and wasps are known to occasionally re-use nests of other species and this may be the case for the tunnel with the partial mud plug. Osmia albiventris nests that we opened were fully lined with chewed vegetation covering the cocoons.
Hole Sizes
Bee Atlas nests were primarily found in a 3/16" tunnels (lower column 3). Some nests were in 1/4" tunnels (upper column 2) and 1/8" tunnels (upper column 3). Medler (1967) found 3 nests, all in ~1/4" diameter tunnels.
Voltinism
Univoltine, meaning they complete one generation per year in Minnesota. Both males and females overwinter as adults inside their cocoons.
Activity Period
Osmia are among the first bees of the year (frequently in May). Information from a small number of Osmia albiventris nests in Medler (1967) suggest nests are completed in early-mid June. Bee Atlas volunteers recorded nesting activity in June, with nest completion dates in July in St. Louis Co.
References
Medler, JT. 1967. Biology of Osmia trap nested in Wisconsin. Annals of the Entomological Society of America, 60(2): p338-244.
Minnesota Record Map
These data are from the Minnesota Bee Atlas project.
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