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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Busy by day but what do mason bees do at night? Mason bees - Osmia spp.


Now that’s a lot of pollen.


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

For the past three months, we’ve had tropical adventures to discover fascinating new arthropods while most insects in Maryland were hunkered down in their overwintering redoubts. But with temperatures reaching the 60s and 70s over the past week or so, the vanguard of the insect class of 2019 has arrived in the form of mason bees. 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. The food 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 looked like at 9:30 on Monday morning, April 8, 2019. Busy bees!

A recent visitor to my mason bee colony remarked how energetic these bees were during daylight hours but wondered what busy bees did at night. 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 a 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.

Hit the lights! 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, emerges and performs a 180-degree pirouette, before reentering the chamber rear end first. After unloading pollen, it’s off to collect another load.


“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.