Mason Bees

An often-heard concern each spring and summer is “bees are destroying my house!” Residents of older buildings will notice bees industriously excavating their south-facing brickwork, and understandably worry that this will compromise the building.

These bees are one of the several species of mason bees in the UK. The commonest is the red mason bee (Osmia bicornis). The red mason bee (like most bees) face a range of pressures, including habitat loss, pesticides, disease and climate change. They are hugely important pollinators of our crops and flowers, the red mason bee being particularly effective at pollinating fruit trees.

Unlike honeybees and bumblebees, mason bees are ‘solitary’, meaning neither living in colonies nor having workers. Once mated the females cleans out an existing hollow (e.g. gaps in window frames, roof tiles or airbricks ) or excavates one from soft mortar or sandy material.

Red mason bee

Within these tunnels she moulds a series of cells, laying an egg in each, fills with pollen and finally sealing with mud. Over the year, eggs develop via larvae and pupae into an adult bee – digging their way out the following spring to begin the cycle again.

Most of the time, the effect of mason bees is inconsequential. They are often attracted to a wall because its’ mortar is very old and/or in poor, soft condition. In very large numbers however (and/or with unmaintained pointing) they can lead to significant damage, particularly if there is water ingress.

Why not try to give them an alternative nesting place besides your house by installing a bee hotel. These need to be in a sunny sheltered spot, > 1m off the ground and near a rich source of flowering plants.

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