A mason bee (Osmia sp.) (Photo Credit – Wikimedia Commons)
Image by A mason bee (Osmia sp.) (Photo Credit – Wikimedia Commons)

Know Your Mason Bees

These solitary bees, which make up about 7% of 400 New York State bee species, are very important pollinators.Many of them prefer to nest in hollow plant stems, cavities or dead wood.They are very, very gentle.The name mason bee comes from their use of mud as part of their nest building.In New York state, they are represented by the genera Osmia, Hoplitis, Chelostoma, and Heriades.Generally these are smaller bees and they are often dark in color.These bees have one generation per year.One type is specific to mock orange (Philadelphus) only, but make sure you avoid the double flowered varieties because these may not provide as much nectar and pollen as the straight species.Resin bees, Heriades, may nest in drilled out blocks of wood (you can find specific designs and instructions how to build these, if you are interested).

In spring, after the temperature hits a consistent high of 55 degrees F, both males and females emerge.They mate immediately, the male dies, and the female begins nest building within 3-4 days. This is why it is helpful for early flowering pollen and nectar sources to be very near their emergence point, that way they use less energy in their early foraging.Next year’s bee size depends on how much nectar and pollen the female is able to gather during the current season.Don’t judge by a name, some of these important early flowering plants may normally be considered weeds.

The females use cavities already present, such as hollow stems from large plant stalks, so be careful to leave some for the bees! Wait until temps are consistently 55 in the spring and observe for bee and pollinator activity before cleaning up.Do not discard the stems because they can be gathered and used to make mason bee houses.Bundle and tie them together, plug one end of the stems with a little mud, and hang so that the open ends are facing southwest to west and angled toward the ground a little so that they do not fill up with water.Place near garden areas that need pollination and away from birdfeeders or areas of high bird activity.

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Last updated April 13, 2021