Mason bees herald the arrival of spring: Horned-faced and Blue orchard mason bees, Osmia spp.

Mason bees herald the arrival of spring: Horned-faced and Blue orchard mason bees, Osmia spp.


Male mason bees are the first to emerge each spring and as females make their appearance, the mating game begins!


Now that’s a lot of pollen!

After a somewhat dreary and rather chilly end of winter, the ides of March arrived with temperatures in the 60s and 70s here in the DMV. As in years past, this triggered the emergence of this season’s vanguard of mason bees, awakened from their winter slumber just in time for the first day of spring. Several years ago, I established a colony of mason bees by purchasing about 30 hollow cardboard tubes from a purveyor of bee paraphernalia. These tubes were rapidly colonized by grateful hordes of bees and now the colony occupying my car port numbers in the hundreds. Mason bees are solitary bees, meaning they lack the well-known social structure of honeybees where a queen mother rules the colony. In the world of my mason bees, every female is a queen tasked with providing food for her own daughters and sons. Although each female is solely responsible for raising her own young, they are gregarious and will happily live in close proximity to one another, sometimes establishing colonies of hundreds of bees each with her individual nest.

Watch as a male horned-face mason bee emerges from his bee-tube-nursery and takes his first steps into the sunlight. Next on the agenda, find a mate.

Mason bees fill each tube with glorious yellow pollen cakes, food for their developing offspring.

The food each female provides consists of pollen cakes, nutritious balls of pollen and nectar gathered from Mother Nature’s first blossoms of spring. Mason bees provide the valuable ecosystem service of pollination. High on their list of favored plants are some of my favorites as well, apples, cherries, and blueberries. In a fascinating study, Drs. MacIvor, Cabral, and Packer found that in addition to insect pollinated plants, some Canadian mason bees collected significant pollen from wind-pollinated trees including oaks and birches, and the ubiquitous lawn weed, white clover.

This is what my carport looks like on springtime mornings when mason bees are busy collecting pollen.

Mason bees are remarkably energetic during daylight hours but I was curious to see what they did at night. Who wouldn’t be? One way to find out, grab a flashlight and have a look. In the middle of the night, mason bees rest near the entrance to their brood chamber. Their abdomen faces outward and is flexed downward, creating a formidable barrier barring access to the pollen cakes and brood beyond these hard-working mothers. Like many other bees we have met in Bug of the Week, mason bees are gentle and not at all interested in stinging humans. Nesting materials for mason bees can be purchased commercially and I highly recommend creating habitats for these industrious and fascinating pollinators.   

At night mason bees rest, rear ends facing outward perhaps to block intruders from entering their galleries. With the morning sun, the colony springs to life with brown horn-faced bees and blue orchard bees shuttling pollen from blossoms to their brood chambers. Check out the mason bee almost dead center at about one minute and thirty seconds in the clip as it enters a brood chamber head first, then performs a 180-degree pirouette, before reentering the chamber rear end first. After unloading pollen, it’s off to collect another load.


The interesting article “Pollen specialization by solitary bees in an urban landscape” by J. S. MacIvor, J. M. Cabral, and L. Packer Singer was used as a reference for this episode.

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