Last Updated on September, 2024
Masonry bees, commonly confused with Honeybees, live alone and make their nests in small holes, often in brick-and-mortar walls of houses. This has led many homeowners to worry that these bees can damage their homes.
While Masonry bees are great for pollination, their nesting habits might cause some concerns about the safety and upkeep of buildings.
In this article, we will examine what masonry bees do, where they nest, and whether they can harm your home. This will help homeowners understand these bees better and know what steps to take, if needed.
Quick Summary
- Masonry bees are solitary insects that make their nests in holes, cracks, and irregular cavities in walls and can potentially damage buildings.
- While masonry bees are not dangerous, their nesting habits can cause structural damage over time, and homeowners can take preventative measures such as repointing mortar and providing alternative breeding sites to minimize the risk.
- These bees are efficient pollinators and play a vital role in plant and flower reproduction.
Do Masonry Bees Damage Your Home?
Masonry bees, also called mortar bees, usually nest in existing holes, cracks, and irregular cavities in walls, so they don’t often cause severe damage to buildings or property.
They can be found in old nail holes, gaps in stones, beetle borings in wood, spaces under roof tiles, and even inside locks.
Though they live alone, female Mason bees are attracted to places where other females are present and already breeding. Some can dig into softer material with their jaws.
There are different types of Masonry bees in the UK, and all can cause some level of damage to structures. Most of the time, masonry bee damage is minor, but sometimes, it can be serious enough to need expensive repairs.
Even though these bees are solitary, they tend to return to the same place where they were born, so their numbers can build up in one area over many years. Most homeowners don’t notice the damage from Masonry bees until they move into a new property.
Inspections might miss signs of masonry bee activity, especially if done during cold or rainy weather. As more bees hatch, more bees will use the same entry points, creating more nests.
Over time, this can weaken a building’s waterproofing, letting in water and pests. Moisture can cause more damage, especially in freezing weather, which creates more opportunities for bees to nest.
While Mason bees usually cause only minor damage to buildings, they can significantly harm plants in a yard. They cut small sections of leaves, which can hurt plants if done extensively and quickly.
Damaged leaves affect a plant’s ability to make food, which can lead to the plant dying if too many leaves are lost.
What are Masonry Bees?
Masonry bees, also known as Mason or Mortar bees, do not live in colonies like Honeybees. Instead, they nest in individual holes in the ground and occasionally in walls, particularly in mortar joints, soft bricks, stones, or cob.
In Britain, there are almost 20 species of these bees, the most common being Osmia rufa, also known as the Red Mason bee. They prefer sunny, south-facing spots to help their eggs develop.
Masonry bees make their nest in spring or summer, laying six to twelve eggs in individual cells filled with nectar. These are sealed, usually with mud.
The new brood emerges the following year to continue the cycle. Mason bees look similar to honeybees. The females have stings, but are unlikely to use them unless aggravated.
These bees are well known for their tendency to re-nest in old or poorly maintained mortar between bricks in brick homes. They create horizontal, cylindrical holes for their nests.
In addition to walls, they can also rest in roof tiles, window frames, timber, and air bricks, often without causing damage.
There are around twenty species of Masonry bees in the UK, but typically, only six are commonly seen. The population of each species is often very localised, with different areas hosting different dominant species.
How to Identify Masonry Bees?
Identifying Masonry bees involves looking for specific physical traits and behaviours that distinguish them from other bees. Here are key characteristics to help you identify Masonry bees.
Physical Characteristics
- Size and shape – Mason bees are similar in shape to honeybees, measuring about 10-15 mm in length.
- Colour – They often have a reddish brown or orange-brown colour, especially the red Masonry bee (Osmia rufa), which is common in the UK.
- Body features – They have a robust, slightly furry body. Females have noticeable hair on the underside of their abdomen for carrying pollen.
- Wings – Their wings are clear and well defined.
Behaviour
- Solitary nature – Unlike honeybees, masonry bees do not live in large colonies, and you will see individual bees rather than swarms.
- Activity period – They are mostly active in spring and early summer when breeding and laying eggs.
- Flying patterns – Mason bees have a more erratic flying pattern than honeybees, and tend to stay close to their breeding sites.
Signs of Masonry Bees
- Small piles of dust – You might find small piles of dust from affected mortar beneath holes where they are nesting.
- Deposits – Since female Masonry bees carry pollen, you might notice deposits near breeding sites.
- Masonry bee traffic – Increased mason bee traffic around specific areas of your home, especially in warm, sunny weather, can indicate their presence.
Other useful guides:
Masonry Bee Life Cycle
Mason bees have a yearly life cycle that involves the following stages:
- Nesting and egg laying (spring to early summer)
Nesting: Females find sunny, south-facing holes in walls, bricks, or wood.
Egg laying: They create cells, fill them with nectar, lay one egg per cell, and seal them with mud.
- Larval stage (summer)
Hatching: Eggs hatch into larvae within a few days.
Feeding: Larvae consume the pollen and nectar mixture, growing over several weeks.
- Pupal stage (late summer to autumn)
Transformation: Larvae spin cocoons and become pupae.
Development: They develop into adult bees and remain in cocoons through winter.
- Emergence – (spring)
Adult bees: New adults emerge in spring by chewing through the mud seals.
Mating: Males emerge first, mate with females, and then die. Females start the cycle again by breeding.
- Adult mason bee life
Reproduction: Females lay eggs in new nests. Adults live for a few weeks, focusing on reproduction.
Are Masonry Bees Dangerous?
Mason bees are generally not dangerous to humans or pets. Here’s a concise summary:
Stinging: Female bees can sting, but they are very docile, and rarely do so. Male bees cannot sting.
Aggressiveness: They are non-aggressive, and do not defend their nests
Allergies: Stings are uncommon, but individuals allergic to masonry bee stings should be cautious.
Structural masonry bee damage: Breeding in mortar joints and soft materials can cause minor to significant damage to buildings.
Pollination: They are efficient pollinators, aiding in plant and flower reproduction.
When are Masonry Bees Active?
These bees are most active from early spring to mid-summer (May to July). During this period, they are often mistaken for honey bees and wasps. Occasionally, a second brood may appear in September, depending on the weather conditions.
Preferred Conditions
Sheltered, south-facing walls and roofs: Masonry bees favour locations with consistent sunlight.
Sunlight and activity: Their activity increases with sunlight. Bees are highly active when the sun is out and tend to disappear quickly when it goes in, leading to intense but short periods of activity.
Common Nesting Places
Location: Look for nests in old or poorly maintained mortar, soft bricks, stone walls, cob, and other building crevices. They also nest in existing holes in wood, roofs, and window frames.
Breeding sites: Nests are often found in sunny, south-facing areas which provide the warmth needed for egg development.
Holes: They use or create horizontal, cylindrical holes. You may notice these in mortar or other suitable crevices around your property.
Mud seals: Mason bees seal their nest holes with mud or other materials, which can clearly signify their presence.
While they are most noted for breeding in walls, mason bees can also be active on roofs, creating nests between and under tiles with minimal damage.
However, when a large number of bees target the mortar of stone and brick walls, they can become a significant issue, particularly if their populations increase over time.
How to Control or Treat Masonry Bees?
To manage masonry bees:
- Clean out affected mortar joints to a depth of 15mm and repoint them. To prevent females from returning to their nest sites, this is best done in summer or autumn.
- Use mortar mixes that aren’t too strong for the bricks or stone, but are hard enough to deter the bees.
- Fill in galleries and burrows using a mortar gun using a wetter-than-usual mix to ensure the mortar flows into the spaces.
- Add a water-based insecticide to the mortar mix. This is sometimes done in spring to protect the mortar from bees before it hardens.
- Reapply a protective lime render to walls if bees burrow into the stone. Limewash alone usually isn’t an effective deterrent.
- In spring, cover walls with fine netting to prevent recolonisation of bees by finding breeding sites.
- Place artificial nesting boxes near walls to attract bees away from the structure. These can be homemade from dried clay soil indented with holes, or purchased pre-made kits made from eco-friendly materials.
- If bees are breeding bricks or stones, chemical treatment might be necessary. However, this method isn’t effective in the long-term, may stain masonry, and isn’t made of environmentally friendly materials. It may be a final resort if other methods fail.
Conclusion
While mason bees don’t pose a direct threat to humans or pets, their nesting habits can cause structural damage to your house or your property over time.
By taking proactive measures such as repointing mortar, using protective netting, and providing alternative breeding sites, homeowners can minimise the risk of damage while preserving the vital role of these bees in pollination.
With careful management, it’s possible to coexist with these bees without compromising the integrity of your house.
