You might first notice them when they look like they are doing a disappearing act, or sometimes it can seem that there is a large swarm of bees near your house. If they are mating they seem to be flying frantically, and can look very scary. What they are actually doing is using an existing hole where the mortar is broken to make a long tunnel where they can complete their life cycle. This is typically in between a brick or window sash or under roof tiles.

Masonry bees are more active from early spring to mid-summer and are commonly confused with honeybees and wasps. In the UK, there are around 20 species of masonry bee. They prefer sheltered, south-facing walls and roofs that get a lot of sun and the bees can appear or disappear very quickly. If the sun is out, the bees will be too, but as soon as it goes, so do the bees.

Over time, the number of masonry bees will increase in the affected mortar. Although they are solitary creatures, they do seem to re-nest in the same place, so a masonry bee family can be there for years. As each new brood matures, higher numbers will be sharing the same entry hole, but using different individual nesting chambers. Each cell within a brood chamber contains between one and three eggs that hatch into larvae and develop over the coming months to emerge in the autumn or following spring.

In most cases, masonry bees do little damage to property but if left, the holes can lead to other animals and water getting into your property. And if not treated, you could literally be looking at a huge infestation, which is a much bigger problem to solve.

This means that treating the situation is easier to do when you first notice it, as each hole will need to be filled or treated. If you have a serious infestation, you could be looking at several hundred holes and you will need a specialist who will use insecticides and fast setting mortar, which will be applied using a long pointing gun to fill the narrow, deep holes.

Repairing the mortar and filling in the holes is what is needed, so call in a pest control company to check and sort the situation. They may well check the problem in summer or when the sun is out, treating the problem as the months get cooler.

If you do notice some activity, leave well alone. The masonry bee has a sting, which will hurt. Watch from afar and if you are concerned or if you have young children, call in an expert.