Mortar Bees

Mortar Bee - Infographic

These bees are mostly large and have coloured bands across the abdomen. They normally make their nests in banks of hard soil or sand and, when near the coast, in the crevices of rock faces. In urban environments brick houses and those with brick foundation walls, which have poor quality mortar may be damaged by the female mortar bees that often make their burrows deep into the mortar. Each female makes its own burrow, but it may be part of a complex of separate burrows in the mortar. The female lines the burrow with lax-like material and this gives some protection to the young that are reared in the burrow. They prefer to stay near walls that receive sunshine for much of the day. Mortar bees are harmless as they are not aggressive and will not sting people.

Mortar bees are also known as masonry bees because they like to nest in crevices or holes in masonry. This species of bee has enlarged rear legs, used to remove mortar from joints of brickwork. Mortar bees prefer to work in the softer mortar mixes and can cause significant structural damage. When a mortar bee removes the mortar from the joins of brickwork, this enables moisture to enter the wall cavity and can cause some areas of collapse of brickwork when the damage is advanced.

Any brickwork with soft mortar (especially mortar with a high lime or sand content) is susceptible to mortar bee attack. Additionally the colour of brickwork is often associated with mortar bee attack, as lighter bricks will often have a softer mortar with less cement content to match the colour of the bricks. Blonde bricks and terracotta coloured brickwork appear to have a higher occurrence of mortar bee attack than bricks with a darker finish. Normally once signs of mortar bee damage are located the mortar bees are always considered to be active.

While mortar bees do excavate mortar from joints of brickwork, they are more of a symptom of a problem being soft mortar. Insecticidal control is of little permanent value and must be repeated annually. As a result the most effective treatment is to fix the problem directly, through repointing the mortar joints of the brickwork with a new mortar that may contain a higher percentage of cement or rendering the wall. This will make the mortar to hard for the mortar bee to effectively remove with its hind legs.