Can masonry bees seriously damage buildings?
A few holes will not cause serious damage to a building, bees will use existing holes and crevices even beetle holes in timber, as well as spaces under roof tiles, behind ventilation grilles.
However, solitary, females are attracted to sites with other females present, and may also burrow mortar joints. They use their jaws to excavate or enlarge holes, kicking out spoil behind them. The yearly burrowing activity may over several years cause a reduction in the bearing capacity of cement or bricks that could fill with water which might expands on freezing.
Should I control masonry bees?
Where a large number of masonry bees threatens the fabric of a building it might be necessary to take action. If there are numerous nesting holes and large numbers of bees milling around on a wall with bits of mortar dust and brick particles ob the floor below the wall it would be advisable to take remedial action and either repoint the building or erect a fine mesh net to prevent access to the wall until remedial work can be carried out. The provision of artificial nesting boxes on or near walls can help entice bees away from them and prevent recolonisation. These can be home-made from dried clay soil indented with holes or, alternatively, proprietary kits are available manufactured from environmentally-friendly materials.
What should I do about masonry bee damage?
Mortar joints should be raked out to a depth of 15mm minimum and repointed, preferably in late summer or autumn. Masonry bees re-use their natal nest sites, this so this will help break the cycle. New mortar needs to be strong enough to discourage burrowing but not be too strong for the bricks or stone. Galleries and burrows can be filled using a mortar gun with a wetter than usual mix to aid the flow
Should I use chemicals against masonry bees?
A. It is always preferable to find a way to live with bees or to discourage them away rather than killing them, however this isn’t always possible. Contact your local pest control company who will be able to advise you.