Mason bees are named for their use of mud or clay in their nests. They belong in the genus Osmia in the family Megachilidae.
At the Fletcher Wildlife Garden, we have found Blue Orchard Mason Bees (Osmia lignaria) as well as the Heriades pictured below. This and other species in the family are very good at pollinating fruit trees. They are closely related to leaf-cutter bees, which will also use bee boxes.
Life cycle of mason bees
May: Adults emerge in spring around the time apple trees bloom. They mate and lay eggs, provisioning their tunnels with lumps of pollen mixed with nectar and saliva. They seal the
chambers and the whole tunnel with mud, so need a source nearby. Adults live 4‐8 weeks.
Early summer: Eggs hatch, larvae eat their pollen
Late summer: 5th instar larvae pupate
September: Pupae open and adults emerge, but hibernate in their coccoons until the following spring, when the cycle starts again.
Why do they need bee houses?
Mason bees do not dig their own tunnels; instead they look for “natural” tunnels, such as hollow plant stems or twigs or the abandoned nests of other insects. Many of these potential mason bee nests are cleared away from our urban properties in an effort to keep our yard “tidy.”
Bees are also susceptible to parasites and disease. Providing a nest box that can be cleaned or replaced every year may help minimize these and produce healthier bees.
Mason bees are readily attracted to paper tubes. Drilled holes in wood are also an option, but both types of tunnels should be replaced every year.
How to make a mason bee box
Our instructions come from Richard Scarth, who has been helping mason bees for many years. Jenny Sheppard demonstrated the construction of this type of bee box at a workshop in May and donated two boxes to the Fletcher Wildlife Garden.
Please note: this easy-to-make bee box is intended for summer use only. The idea is to open the tunnels in the fall and store cocoons in the refrigerator over the winter. This provides a chance to clean away parasites and increases the chances of bee survival.
Jenny has kindly offered to do a follow-up workshop in the fall to show us how to retrieve cocoons properly and the best way to store them.
Alternatively, you may wish to build a protective structure for your bee boxes and leave them out all year round. In either case, the whole box should be replaced in spring just before the previous year’s adults emerge.
Does it work?
We installed our two boxes in our insect hotel on 7 May 2015. Within a week, bees were busily filling the tunnels with nectar and pollen, laying eggs, and closing up the compartments with mud.