Masonry or Mortar Bees

There are several species of solitary bees which will sometimes forsake their normal habitats of sandy earth banks and soft exposed rocks, to cause damage by tunneling into perished mortar joints, particularly in old buildings. A ‘suitable’ building could attract many bees and give the impression of a swarm.
The damage is caused by the female bees burrowing into the mortar to form galleries, in which they lay eggs and leave a food supply for their young. Over several years, many galleries can be produced and, ultimately, structural damage may be caused. Tunnel construction only takes place in early spring and only a single brood is raised during the year.
These bees are basically harmless as regards stinging

As the bees’ activities are limited to very soft material, re-pointing of the affected areas is the best way of dealing with the problem. This is best carried out in late summer or early autumn. The joints should be raked out to a depth of about 15mm and re-pointed with mortar that is not too strong, eg. a 1:2:9 cement, lime, sand mix or a 1:8 cement/sand mix with a plasticiser added.

The use of insecticides is not to be encouraged, as the bees are valuable early pollinators. However, should the urgency of the situation demand an insecticidal treatment, then an insecticide which is approved for the control of flying and crawling insects (and does not specifically exclude bees) should be sprayed directly into the holes as far as possible. It should be remembered, however, that any such treatment is only a stopgap measure and will not achieve a lasting effect, as re-pointing is the only permanent cure.

When using any insecticide always follow the manufacturer’s instructions and precautions.

The Council does NOT offer a treatment for these bees.