These solitary bees are also often mistaken for wasps due to their size and colouration although like the honey bee they are mire of a light brown and yellow with hairs on their back and head.
They are found in old brickwork and crumbling mortar hence the name.
Even though they live in solitary because they like the same areas to inhabit it will often look like a wasp nest due to the amount living within a single area of brickwork.

The Mortar bee does have a stinger but they will not be able to sting as they are unable to penetrate the human skin with it.
Treating these bees is very hard as there will often be thousands of holes which will all need treating at the same time.
Replacing old mortar will help you avoid getting them every year but most just live with them.